1970 455 block has just come back after re-bore, machining, cleaning and supplied with a freeze plug kit, which included 6 brass plugs, 2 threaded oil galley plugs (with no oil hole!) and 3 steel anodized plugs. One fits on the rear of the block behind the camshaft, one to cover the oil galley plug and the third is a small approx 5/8" (15mm) plug whose location is a mystery to us. It has 19/32 stamped on it.
The crankshaft is in but we do not want to proceed until the mystery plug is identified.
If a member can tell where this small plug lives it would be greatly appreciated.

 

3/8" (9.52mm) is much smaller than 15mm.

 

Corrected. Thank you. But where does the plug fit on the engine?

 

 

My Pioneer catalog says the 19/32" plug is an "oil galley" plug but I have 3 Olds blocks here and I cant see anywhere on any of them where that size plug would go. One possibility is that plug is used in a different Olds engine since that freeze plug kit is sold for all of them, including the diesel ? There are a lot of block plug kits that are like that and have extras in them.

 

I have bought and used many freeze plug kits for Oldsmobile engines over the years, I seem to always have one pipe plug left over. I always assumed it was for the diesel or other less common application.

 

Thanks to the replies and interest, especially to Joe whose picture solved the mystery of where this plug should belong. It seems that this plug is indeed used in other blocks and is not needed in this one. I now feel comfortable in continuing with the build. Thanks again to the forum and interested members.