The Groco 1.5 inch seacock and its male partner a 1.5 inch thru-hull engage a full eleven threads deep within the body of the sea cock where they are hopefully safe from lateral forces. I experimented with the parts today, and eleven threads it is.
Now the question is whether to thru bolt or to "lag the flange down" to the mounting block with screws as Ebb says it. Asssuming a good non-splitting installation with lag screws is there much benefit to taking the thru-hull bolt route instead.
The lag screw method is how my last Groco rubber plug 1.25 inch seacocks were attached. They had two screws each 180 degrees apart. The new seacocks have three bolt holes 60 degrees apart. They were well bedded with lots of sticky stuff and the yard had trouble removing them despite their straight threads. I had to use a very large long handled pipe wrench and a bench vise to free the jagged remains of the severed thru-hull from the sea cock body.
The first photo below shows the Groco seacock with a Conbraco hose barb and a Groco thru-hull. The blue tape marks the part of the thru-hull threads that engage the seacock threads (eleven threads deep).
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