It does sound like bikes use some wacky sizes.... but it surprises me that MB would use a non standard thread on the injectors... thus I am just trying to confirm the size....

Springs can easily maim or kill you . Don't take any chances with them. That does not mean you can not make your own compressors but does mean it should not be your first metal working project....this is pretty much one of those deals where " if you have to ask" you do not have the experience to do it safely. Your health is worth more than you probably realize at your age.... don't take any unnecessary chances with springs.

Even when I am using correct gear.... I use an aircraft cable and tie the spring so it can not come out at me in case something slips or breaks.... " **** happens"... try not letting it happen to your face....

edit, Ok you posted while I was composing... so this is a 22 mm diameter rod with 1mm threads.... so this is a VERY FINE thread for the size of the rod , right ?