oil drain plug 263

[WickedClown]

Does some one know what the correct thread size is for the oil drain plug from a 263 straight 8.

The users manual states 28 mm what is way to big and the suppliers have a 5/8 oversize self treading or a 11/16-20 single oversize.

I had a 11/16-16 plug that is almost the size that fits but the thread is too coarse.

Can somebody help me with this?

[suntreemcanic]

The plug is 18 mm X 1.50 thread. A 1 inch wrench fits the plug perfectly for removal from pan.

[WickedClown]

Thanks for the info.

Did not think it would be metric thread.

[TODD]

There is a typo in the 1950 thru 52 shop manuals showing 28mm threads. Other years show the correct 18mm dim.

In case the search is still going, the GM part number is 1390566. Used on Buicks 1938-58 (exc. 39) and 1956-59 Chevy trucks with the 322 engine.