Corrosion Protection |
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Connectors, including anchors and fasteners, installed in corrosive environments or exposed to corrosive materials, or chemicals, can be damaged possibly resulting in the reduction of load capacity. The selection of the proper connector coating can be a complicated task. Environments can vary greatly regionally and are also influenced by variables such as fertilizer, animal waste, and wet cycle durations. If an electrolyte is present, such as water, a metal will form an electric circuit with a dissimilar metal and galvanic corrosion can take place. Zinc is the metal used in the hot-dip galvanizing process due to its ability to sacrifice itself while protecting the base steel underneath. When the zinc and copper are in electrical contact with each other the copper will have a tendency to extract electrons from the highly reactive zinc at a greater rate, therefore corrosion will take place at a greater rate. That being the case it is impossible to prescribe a reasonable uniform solution which will serve all
environments adequately.
In cooperation with the Environmental Protection Agency, chemical producers in the treated wood industry agreed to discontinue the use of Chromated Copper Arsenate (CCA) for most residential applications at the end of 2003. In place of CCA, treated wood suppliers use copper based alternative treatment chemicals such as Amine/Ammoniacal Copper Quat (ACQ-C, ACQ-D), and Copper Azole (CBA-A, CA-B). Sodium Borate (SBX, DOT) is used primarily in sill plate applications. Testing conducted by USP and others in the industry have concluded the ACQ and Copper Azole wood treatments are more corrosive to metals than traditionally used CCA treatments are.
Recently some wood preservative manufacturers have introduced new wood preservative formulations. These formulations include new micronized copper products as well as carbon based PTI wood preservatives. Testing by USP has found some of these formulations are less corrosive than ACQ and CA-B products, but not necessarily the same as untreated wood.
USP Structural Connectors currently offers four different corrosion resistant finishes to cover a range or corrosion performance:
Triple Zinc (TZ) – galvanizing provides a prefabrication
coating of 1.85 (G-185) ounces of zinc per square
foot of surface area measured in accordance with
ASTM A 653.
Fastener: Hot-dip galvanized fasteners
Hot-Dip Galvanized (HDG) – coating provides an after-fabrication
hot-dipped zinc coating. The coating
thickness is dependent on the connector material,
but generally ranges from 1.1 to 2.3 ounces of zinc
per square foot of surface. Hot-dip products meet
requirements set forth in ASTM A 123.
Fastener: Hot-dip galvanized fasteners
Gold Coat (GC) - gold coat is a proprietary multi-layer protection system. It
is comprised of an organic top coat barrier layer and a zinc layer placed
over a steel substrate.
Fastener: Gold Coat fasteners
Stainless Steel (SS) – is the best option for corrosion
protection. Quality stainless steel (316SS grade
steel) is used to fabricate connectors. Although
costs are higher, some applications may need the
virtual corrosion proof quality of stainless steel.
Fastener: Stainless Steel fasteners
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The coating recommendations listed below have been developed by reviewing both field service performance and accelerated corrosion testing results. While accelerated corrosion testing is a valuable tool to help predict relative performance, both the particular testing method used by the industry and the different wood treatment products tested are relatively new and there is little actual field service life data to correlate to the test results. In addition, actual service environments are much more complicated than accelerated tests. In accelerated tests influencing variables are typically minimized and manupulated to cause reactions to occur more quickly. Consequently, this may result in reactions which are not completely representative of actual service conditions. Because of this it is difficult to assign an expected service life to a given coating in an environment based on the results of accelerated testing.
USP Structural Connectors Coating Recommendations
| UC1 |
Interior construction, Above ground, Dry |
Continuously protected from weather or other sources of moisture |
General framing, interior construction |
Untreated |
G90 |
| UC2 |
Interior construction, Above ground, Damp |
Protected from weather, but may be subject to sources of moisture |
Sill plates |
SBX-DOT, Organic
ACQ-D (0.25), CA-B (0.10), CA-C (0.06), MCQ (0.25), µCA-C (0.05) |
G90
Triple Zinc (G185)8,9 |
| UC3A |
Exterior construction, Above ground, Rapid water runoff |
Exposed to all weather cycles, not exposed to prolonged wetting |
Exposed exterior beams or columns in an open, covered structure |
ACQ-D (0.25), MCQ (0.25), CA-B (0.10), CA-C (0.06), µCA-C (0.05), Organic |
Triple Zinc (G185) or USP Gold Coat |
| UC3B |
Exterior construction, Above ground, Poor water runoff |
Exposed to all weather cycles, including prolonged wetting |
Deck beams and joists |
ACQ-D (0.25), MCQ (0.25), CA-B (0.10), CA-C (0.06), µCA-C (0.05), Organic |
Triple Zinc (G185) or USP Gold Coat |
| UC4A |
Exterior construction, Ground contact, General use |
Ground contact or fresh water exposed to all weather cycles |
Deck posts |
ACQ-D (0.40), MCQ (0.40), CA-B (0.21), CA-C (0.15), µCA-C (0.14) |
Triple Zinc (G185) or USP Gold Coat5 |
| UC4B |
Exterior construction, Ground contact, Critical structural |
Ground contact, fresh or salt water exposed to all weather cycles |
Permanent wood foundations, critical structural members |
ACQ-D (0.60), MCQ (0.60), CA-B (0.31), CA-C (0.25), µCA-C (0.23) |
Stainless Steel |
Notes
1. G90 and G185 refer to galvanization requirements for ASTM A653 material.
2. Connectors galvanized to ASTM A123 may be used in place of either G90 or G185 coatings.
3. Other coating may be suitable for a given environment if the conditions are known and predictable.
4. For G90 or G185 connectors use fasteners galvanized per ASTM A153. For Gold Coat connectors use Gold Coat fasteners, and for stainless steel connectors use stainless steel fasteners.
5. If the enviroment has the potential to contain elements which may make it more corrosive, the use of stainless steel is recommended.
6. MCQ is a micronized copper treatment such as
Micro Pro by Osmose. µCA-C is a dispersed copper treatment manufactured by Arch Treatment Technologies. Organic preservatives include L
3 from Arch Treatment Technologies and EcoLife II from Viance, LLC.
7. For wood treatments not shown contact USP or the wood preservative manufacturer for recommended coatings.
8. Testing by USP has found that in interior applications where the treated wood will remain relatively dry during its service life the use of G90 connectors with MCQ or µCA-C treated wood is appropriate.
The formulations used by wood preservative manufacturers are constantly changing and improving. USP Structural Connectors continues to test new wood treatments as they become available and will continue to update its recommendation as appropriate. Neither the 2006 International Residential Code or 2006 International Building Code specifically prescribe a recommended coating weight or type for connector products such as joist hangers, column caps, etc. In cases such as this we advise following the connector manufacturer's recommendations.
Corrosion Protection Guidelines:
- USP recommends stainless steel connectors for the highest level of corrosion protection. As an economical alternative to stainless steel our new Gold Coat connectors are specifically designed for exterior application when in contact with preservative treated wood.
- Triple Zinc G-185 connectors are available as an economical alternative for exterior applications which will provide a minimum level of protection.
- The use of correct fastener with the connector is critical. Stainless steel connectors require stainless steel fasteners. For exterior applications, hot-dip galvanized fasteners (HDG) must be used with both Triple Zinc and Hot-dip Galvanized finishes. Gold Coat connectors require gold coat fasteners.
- USP's zinc dichromate WS Wood Screws are not recommended for use with preservative or fire-retardant treated wood. Some wood screws are available in Gold Coat.
- USP Structural Connectors clearly differentiates standard G90 connectors from the corrosion resistant connectors. Gold Coat connectors are distinguishable from other connectors because of their concealing color. Following are examples of our carton labels, bin cards for retail displays, and individual product labels.
Corrosion Resistant Products
| 8d (0.131") x 1-1/2 nail |
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NA11 |
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N8-GC |
| 10d (0.148") x 1-1/2 nail |
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NA9D |
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N10-GC |
| 16d (0.162") x 2-1/2 nail |
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NA16D |
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| 8d Common (0.131" x 2-1/2") |
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| 10d Common (0.148" x 3") |
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| 16d Common (0.162" x 3-1/2") |
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N16C-GC |
| 1/4 X 1-1/2 Wood Screw |
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WS15-GC |
| AB126-HDG |
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AB126-HDG |
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| AB128-HDG |
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AB128-HDG |
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| AB1212-HDG |
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AB1212-HDG |
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| LBP12-TZ |
LBP12-TZ |
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| LBP58-TZ |
LBP58-TZ |
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| LBPS12-TZ |
LBPS12-TZ |
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| LBPS58-TZ |
LBPS58-TZ |
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| THR125-HDG |
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THR125-HDG |
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| THR126-HDG |
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THR126-HDG |
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| THR128-HDG |
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THR128-HDG |
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| THR5816-HDG |
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THR5816-HDG |
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| FA3 |
FA3-TZ |
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| PA18 |
PA18-TZ |
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| PA28 |
PA28-TZ |
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| ST1 |
ST1-TZ |
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| ST2 |
ST2-TZ |
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| TA51 |
TA51-TZ |
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| TA71 |
TA71-TZ |
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| TDL5 |
TDL5-TZ |
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| TDX2-TZ |
TDX2-TZ |
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| HTA20 |
HTA20-TZ |
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| HHCP2 |
HHCP2-TZ |
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| LFTA6 |
LFTA6-TZ |
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| RT3A |
RT3A-TZ |
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RT3A-SS |
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| RT4 |
RT4-TZ |
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RT4-SS |
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| RT5 |
RT5-TZ |
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RT5-SS |
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| RT7 |
RT7-TZ |
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RT7-SS |
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| RT7A |
RT7A-TZ |
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RT7A-GC |
| RT8A |
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RT8A-SS |
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| RT10 |
RT10-TZ |
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RT10-SS |
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| RT15 |
RT15-TZ |
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RT15-GC |
| RT16A |
RT16A-TZ |
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RT16A-SS |
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| RT16-2 |
RT16-2TZ |
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RT16-2SS |
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| CBSQ44-TZ |
CBSQ44-TZ |
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| CBSQ46-TZ |
CBSQ46-TZ |
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| CBSQ66-TZ |
CBSQ66-TZ |
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| D44-TZ |
D44-TZ |
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| D46 |
D46-TZ |
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| D66 |
D66-TZ |
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| EBG44-TZ |
EBG44-TZ |
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| KCB44 |
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KCB44-HDG |
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| KCB46 |
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KCB46-HDG |
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| KCB66 |
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KCB66-HDG |
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| KCB88 |
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KCB88-HDG |
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| PA44 |
PA44-TZ |
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| PA44E |
PA44E-TZ |
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PA44E-GC |
| PA46 |
PA46-TZ |
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| PA46E |
PA46E-TZ |
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PA46E-GC |
| PA66 |
PA66-TZ |
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| PA66E |
PA66E-TZ |
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PA66E-GC |
| PAU44 |
PAU44-TZ |
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PAU44-SS |
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| PAU46 |
PAU46-TZ |
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PAU46-SS |
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| PAU66 |
PAU66-TZ |
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PAU66-SS |
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| PAU88 |
PAU88-TZ |
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PAU88-SS |
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| WAS44 |
WAS44-TZ |
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| WAS46 |
WAS46-TZ |
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| WAS66 |
WAS66-TZ |
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| WE44 |
WE44-TZ |
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| WE46 |
WE46-TZ |
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| WE66 |
WE66-TZ |
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| BC400-TZ |
BC400-TZ |
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| C44 |
C44-TZ |
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C44-SS |
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| C46 |
C46-TZ |
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| C66 |
C66-TZ |
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| KCC44 |
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KCC44-HDG |
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| KCC46 |
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KCC46-HDG |
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| KCC66 |
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KCC66-HDG |
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| KECC44 |
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KECC44-HDG |
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| KECC46 |
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KECC46-HDG |
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| KECC66 |
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KECC66-HDG |
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| PB44-6TZ |
PB44-6TZ |
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PB44-6GC |
| PB66-6TZ |
PB66-6TZ |
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PB66-6GC |
| PBC44-TZ |
PBC44-TZ |
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| PBC66-TZ |
PBC66-TZ |
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| PBES44 |
PBES44-TZ |
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PBES44-SS |
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| PBES66 |
PBES66-TZ |
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PBES66-SS |
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| PBS44 |
PBS44-TZ |
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PBS44-SS |
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| PBS66 |
PBS66-TZ |
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PBS66-SS |
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| PCM4416 |
PCM4416-TZ |
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| PCM4616 |
PCM4616-TZ |
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| PCM6616 |
PCM6616-TZ |
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| HUS28-2IF |
HUS28-2IFTZ |
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| HUS210-2IF |
HUS210-2IFTZ |
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| JL24IF-TZ |
JL24IF-TZ |
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| JL26IF-TZ |
JL26IF-TZ |
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| JL28IF-TZ |
JL28IF-TZ |
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| JL210IF-TZ |
JL210IF-TZ |
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| JUS24 |
JUS24-TZ |
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JUS24-SS |
JUS24-GC |
| JUS26 |
JUS26-TZ |
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JUS26-SS |
JUS26-GC |
| JUS26-2 |
JUS26-2TZ |
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JUS26-2SS |
JUS26-2GC |
| JUS28 |
JUS28-TZ |
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JUS28-SS |
JUS28-GC |
| JUS28-2 |
JUS28-2TZ |
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| JUS28-3 |
JUS28-3TZ |
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| JUS210 |
JUS210-TZ |
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JUS210-SS |
JUS210-GC |
| JUS210-2 |
JUS210-2TZ |
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JUS210-2SS |
JUS210-2GC |
| JUS210-3 |
JUS210-3TZ |
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| JUS44 |
JUS44-TZ |
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| JUS46 |
JUS46-TZ |
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| LSSH15-TZ |
LSSH15-TZ |
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LSSH15-SS |
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| LSSH210 |
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LSSH210-SS |
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| SKH26R/L |
SKH26R/L-TZ |
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SKH26R/L-SS |
SKH26R/L-GC |
| SKH28R/L |
SKH28R/L-TZ |
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| SKH210R/L |
SKH210R/L-TZ |
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SKH210R/L-SS |
SKH210R/L-GC |
| A3 |
A3-TZ |
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| AC5 |
AC5-TZ |
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| AC7 |
AC7-TZ |
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AC7-GC |
| AC9 |
AC9-TZ |
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| JA1 |
JA1-TZ |
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| MP34 |
MP34-TZ |
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MP34-SS |
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| MP4F |
MP4F-TZ |
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| MP5 |
MP5-TZ |
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| MP7 |
MP7-TZ |
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MP7-SS |
MP7-GC |
| MP9 |
MP9-TZ |
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MP9-GC |
| MPA1 |
MPA1-TZ |
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MPA1-SS |
MPA1-GC |
| RSPT4 |
RSPT4-TZ |
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| RSPT6 |
RSPT6-TZ |
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| RSPT6-2 |
RSPT6-2TZ |
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| SPT4 |
SPT4-TZ |
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| SPT6 |
SPT6-TZ |
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| SPT22 |
SPT22-TZ |
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| SPT24 |
SPT24-TZ |
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| SPTH4 |
SPTH4-TZ |
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| SPTH6 |
SPTH6-TZ |
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| KRPS22 |
KRPS22-TZ |
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| L6 |
L6-TZ |
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| MSTA9 |
MSTA9-TZ |
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| MSTA12 |
MSTA12-TZ |
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MSTA12-SS |
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| MSTA15 |
MSTA15-TZ |
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| MSTA18 |
MSTA18-TZ |
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MSTA18-SS |
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| MSTA21 |
MSTA21-TZ |
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| MSTA24 |
MSTA24-TZ |
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MSTA24-SS |
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| MSTA30 |
MSTA30-TZ |
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| MSTA36 |
MSTA36-TZ |
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MSTA36-SS |
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| PS218-HDG |
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PS218-HDG |
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| PS418-HDG |
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PS418-HDG |
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| PS720-HDG |
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PS720-HDG |
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| RS150 |
RS150-TZ |
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| T6 |
T6-TZ |
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| LTW12 |
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LTW12-SS |
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| LTW18 |
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LTW18-SS |
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| MTW12 |
MTW12-TZ |
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| MTW16 |
MTW16-TZ |
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| MTW20 |
MTW20-TZ |
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MTW20-SS |
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| CSH-TZ |
CSH-TZ |
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| DC50-TZ |
DC50-TZ |
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| ERB24-TZ |
ERB24-TZ |
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| FB14-TZ |
FB14-TZ |
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| FB23-TZ |
FB23-TZ |
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| FC24-TZ |
FC24-TZ |
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| FRB24-TZ |
FRB24-TZ |
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| ICPL58 |
ICPL58-TZ |
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| ICPL516-TZ |
ICPL516-TZ |
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| PRT2-TZ |
PRT2-TZ |
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| SCA9-TZ |
SCA9-TZ |
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SCA9-GC |
| SCA10-TZ |
SCA10-TZ |
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| SDJT14-TZ |
SDJT14-TZ |
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| SDPT5-TZ |
SDPT5-TZ |
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| SDPT7-TZ |
SDPT7-TZ |
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Literature & Links for Canada
