Manufactured inhouse by Merimarine LLC in Deltaville USA with a cnc router machine 1/2 inch thick fiberglass seacock /thru hull backing plates.
For use with both Groco and Buck Algonquin Flange Valve line and thru hulls.
Forespar Marelon valves require different backing plates which we also make and list on eBay. 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, polyester, vinylester resins and 5200 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 FROM THE OPTIONS LIST.  PRICE IS FOR EACH BOLT AND YOU WILL NEED THREE PER BACKING PLATE. Note: The BP-2 requires 3/8"-16 bolts which we do not carry.

Just install the valve with bronze bolts directly to the backing plate cutting / grinding off any of the bolts that protrudes through. After adjusting valve to desired position and grinding the backing plate to fit your hull curve dry fit the thru hull as often they need to be shortened to fit properly. Insert the thru hull 3 or 4 threads. Smear some thickened epoxy between hull and plate and tighten the thru hull. This prevents any epoxy getting into the fitting. Thickened epoxy will also fill any slight hull curvature.

Product Name Our Price Fits Seacock Sizes OD (in) ID (in) Bolt Circle (in) Threads
BP-0.75 $30.00 0.750” 4.3 1.05” for 3/4" NPS external thread 3.12 / 3.38 5/16"-18
BP-1.00 $30.00 1.00” 4.3 1.3" for 1" NPS external thread 3.12 / 3.38 5/16"-18
BP-1.25 $30.00 1.250” 5.4 1.65” for 1.25" NPS external thread 3.62 / 4.5 5/16"-18
BP-1.50 $30.00 1.50” 5.4 1.9" for 1.5" NPS external thread 3.62 / 4.5 5/16"-18
BP-2.0$50.002.0”7.0”2.5” for 2” NPS external thread53/8” - 16

BP - 2.5 $50:  Bolt circle: 5.88" (149.35mm), 7" OD, 2.77" ID, tapped threads for 3/8" - 16 bolts