Just be aware that none of the Bilstein, Koni or Boge/Sachs factory struts actually had any “inserts” as such. When you fit new inserts into them you basically gut the factory strut, it comprises a piston, some seals and hydraulic oil, then you fit an actual insert.

Appreciate the feedback, my biggest concern was whether or not the ID of the Bilstein strut was the same as the Sachs or Konis to allow me to do the modification. Seems not too many 944s came with the Bilsteins from factory.

It’s a 1986, there is no gland nut nor a pressed and crimped cap... just a nut at the bottom.

Your 86 944 should have a threaded cap, 87 on 944’s had a crimped cap. If you don’t have a cap and instead have a nut at the bottom of the strut then your struts have been previously rebuilt and therefore are not stock anymore.

The Bilstein conversion inserts required the struts to be cut and a new threaded cap welded on, whereas to fit the Koni inserts you cut then drill a hole at the base to secure with a bolt, so there is no threaded cap. You stated you don’t have a cap but you do have a bolt at the base, it sure sounds like your struts have been cut and fitted with Koni inserts. Post a picture like Jason said, otherwise we could speculate all day long about what we think you have.

Sorry in a rush but here is a quick pic, the actual strut is stamped bilstein. I don’t think they were ever rebuilt like everything else on the car.

As you can see at the top of the shock body the bend thread is why I have to rebuild