Lots of answers but not to your question (I hate wen that happens to me!)

The answer is: 22mm x 1.5mm pitch

I know because I destroyed the threads in my angled pre-chambers and had to run a tap through them. Do not try to use old style injectors and PC slotted collar nuts with newer angled PCs! I didn't know they were angled and after putting a $1600 rebuilt #17 head on my '87 300TD I didn't want to buy new injectors and thought the only difference was the PC nuts. Wrong! Anyway I was actually able to re-cut the threads and so far they are holding a seal. I tried to find the angled PCs used and new.... not available aftermarket. Some websites claim to have them but the PNs are the same as older version... BS. I didn't even try the dealer.. too scared to know the price. After reading as much as I could find (shoulda done that beforehand!) I kinda doubt that the angled PCs make that big a difference... just a little better mixing of the fuel. Also, if you are doing a custom mod remember to check depth of PC in combustion chamber of your engine... you don't want the piston to hit the PC... it can! Here is a link to some MBZ info on the two PCs: http://w124-zone.com/downloads/MB%20CD/W124/Index/602_603/01General.htm Read 01-416 & 01-417 under "Cylinder heads, precombustion".