16mm nipple, nominal size with 16x1.5mm thread pitch FPN 106227 I'm replacing a couple of these on the two QV engines I'm doing. Likley, you'll have to machine them out, as they tend to fuse themselves into the heads. Best, David
You might have been thrown off trying to find a replacement because the threads are not NPT or even tapered pipe threads of any kind, they are standard bolt threads. Probably pretty hard to find outside the OEM suppliers.
You want to replace the OEM one, with one from Hill Engineering that Ricambi sells...it's stainless instead of the original casting...... As noted getting it out and saving the threads in the head is the challenge!
