I need to find the size of the hole of the fitting shown in the picture below. This fitting screws into the front of the head on any GMC 228/236/248/256/270/302. The other end of the tubing attaches to a fitting that mounts low on the driver's side of the front of the block. The line supplies oil from the main gallery in the block to the head. The small size of the hole restricts flow to the head.

Any of you have one lying around that you can measure? Doesn't need to be exact. What is the largest drill bit that will slip in?
Attachments
Oil Restrictor.jpg (3.78 KB, 87 downloads)

Last edited by Bill Hanlon; 01/07/2026 8:56 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.