Hi guys. I just bought bilstein B4 (for 325) and when i take out the old one (Sachs) i found it is smaller at the end.

And the problem is when i put the new one (not so new), i cant tighten it because its bigger than before and the cap is thick . I dont know wether i need to replace the cap or cannot use the absorber. If need to replace the cap, where i can find it?

Please help, need your opinion & suggestion.