300 coolant plugs

Does anyone know what size thread I'd need for the block coolant drains on a 1964 300? 1/8 NPT goes in one rotation which makes me think it may be a 3/8 straight thread of some kind.

 

Those are 1/8" NPT. Maybe yours has crud in the threads?

Jim

 

I'll check it out again, the block was cleaned very well, but I don't doubt something could still be stuck in the thread. 1/8 npt is 1/8 npt right? There's no changes in pitch?

 

GM has always used 1/8" npt.

Get yourself a tap to clean the threads up .

 

Thanks, will do

 

tap cleaned the threads out perfectly. The 1/8 npt went in no problem now, thank you both