Groco Flange Valve backing plate

Description

We will refund any extra shipping fees the day of shipping if ordering different sizes separately but shipped together.
We are manufacturing in house with a cnc milling machine 1/2 inch thick fiberglass seacock backing plates typically used with the Groco Flange Valve line and thru hulls. These are produced from Extren 525 which is water proof, fire proof, mass produced polyester fiberglass sheet with a 30 thousand PSI compression and tensile strength. Epoxy will bond to it.
The seacocks and through hulls can be purchased from West Marine and Defender.com and many others.
These have the same bolt patterns as the Groco BB1, BB2 and BB3 backing plates without the inserts as they are drilled and tapped. The inside diameter of the hole is specific for each thru hull size but by having 6 bolt holes and not 3 you can use the 1" for the 0.75" thru hull and the 1.5" for the 1.25" thru hulls if needed.
We believe that Groco backing plates are made from injection molded pvc which does not bond well with epoxy and also they use brass, not bronze inserts which can corrode. Our prices are typically close to 1/2 the price of Groco backing plates as we only sell direct.
We suggest using Silicon Bronze bolts. Our listing option is for 5/16-18 x 1" long.  THESE BOLTS ARE NOT INCLUDED IN THE COST OF THE BACKING PLATE.  THEY MUST BE PURCHASED SEPARATELY.
Just install the Groco valve with bronze bolts directly to the backing plate. After adjusting valve to desired position and cutting off any of the bolts if they protrude through the backing plate insert the thru hull a couple of threads. Smear some thickened epoxy between hull and plate and tighten the thru hull. This prevents any epoxy getting into the fitting. T
hickened epoxy will also fill any slight hull curvature.
Install as a dry fit first. If the backing plate needs to be sanded to fit the curvature of the hull, orientate the valve correctly first and mark off the correct section to sand with very course sand paper or file. A belt sander works well.
Product Name
Fits Seacock Sizes
OD
ID
Bolt Circle
Threads
BP-0.75
0.750”
4.3
1.05” for 3/4" NPS external thread
3.12 / 3.38
5/16"-18
BP-1.00
1.00”
4.3
1.3" for 1" NPS external thread
3.12 / 3.38
5/16"-18
BP-1.25
1.250”
5.4
1.65” for 1.25" NPS external thread
3.62 / 4.5
5/16"-18
BP-1.50
1.50”
5.4
1.9" for 1.5" NPS external thread
3.62 / 4.5
5/16"-18