The weldement
Another view on this most horrible object. I'm not disputing anything, other than just posting what I hope is relevant information. I came across this weldement, (I think that's what it's referred to), because I mercifully did not have to install it. I drilled and tapped out the old one, an equally terrible job.
So, the base is 1" X 1 1/4" X 1/8". It's exactly 1" deep, with a 5/16" X 1 1/4" bolt. The outside diameter is 1/2" exactly. I used digital calipers for these measurements, but left in a vernier scale caliper just for visual reference. (I've not met anybody in 20 years that knows how to accurately read one of these things). The bolt is obviously stainless, as is the weldement. Do not use a carbon steel bolt on this, as you will insure it very early, and catastrophic demise.
As in, the keel leaving the boat straight down, and possibly taking the winch through the bottom of the boat with it. I've never heard of this happening, but there is no reason to think that it couldn't.