Standard 5/8-18 UNF cap screw in a 216 water temp port here:
http://www.pbase.com/dennygraham/image/162201936 No reason this couldn’t be cut short and a fiber washer used under the head to seal it if
that’s the objective.
Or the end could be turned on the lathe to match the seat and a dead soft copper washer
place in the seat to seal it at the end
Don’t quite know what the problem is with the ½”-14 NPTF in the 235 head. Any standard
½”-14 NPTM fitting could be used to plug it or adapt it. Here a ½” nipple could be capped:
http://www.pbase.com/dennygraham/image/162201937 or in the next one:
http://www.pbase.com/dennygraham/image/162201938 a pet-cock could be installed or a standard ½”to ¼” reducer bushing
could be tapped for a 5/8-18 UNF thread to seal it up or a standard ½ to 3/8-18 NPT
reducer bushing will even take a 5/8-18 UNF cap screw with a fiber washer. And of course
if you need to use the mechanical bulb in your 235 there is always the adaptor that has
been linked to a dozen time here. It the problem is using an electric sender in you 216
head, then a 5/8-18 cap screw drilled and sealed with a copper washer in the seat and with
a ½ NPTF bushing brazed to the head would work just fine.
With all those tools in that shop of yours Deve, I'm sure
you have a lathe somewhere in the shop, make an adapter from
a piece of round stock to take a 1/2 NP and thread the end
with a die to 5/8-18 UNF.
dg
