Checking An Internal Thread Pitch

If the hole is vertical, naturally it will want to run down and fill the hole. I have sprayed cooking non-stick stuff in the hole and as the plaster is setting, inserted a u shaped loop of wire, sometimes a paperclip, depending on size, and it will simply unscrew. I make sure the hole is very clean, and use a little air to make sure the spray is pretty dry before doing this. And of course, there can be no features that will entrap the plaster. Ideally, the part can be oriented to put the feature horizontal.

Bill, I worked inspection for a few years, and that's where I picked this method up. A QC guy with Dresser Industries put me onto it and got me the box of plaster. It goes a long way.

MSC and several others sell a 2 part replica rubber compound just for this if you want to get official. :)
 
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