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It's gonna happen, no matter how many times you have told yourself "I wont buy any more lenses" you end up relapsing. After the relapse you end up needing lens caps, lens hoods etc for your newly acquired (your temporary fix) lens. Haha, in all seriousness I got tired of buying rear end lens caps that wouldn't stay on tight enough. I found these to act, feel and look almost as good as the oem for a tenth of the cost. Hope this helps you guys with your post LBA purchases.
Hinterer Objektivdeckel Rear Lens Cap Cover for Pentax PK 18 55mm 55 300mm 40mm | eBay