Wow, not good news since I own one of these too. Did you try emailing Quicker about the broken cap? Most companies who want to stay in business will send a new part for free or at least sell you one. You could try these guys too since they seem to be the only consistent US sellers. http://www.velo-orange.com/quickerpropump.html The threads measure out to 29mm OD or roughly 1.11'' (1 5/32"). If you have any machinist friends who wouldn't charge you $50 to fabricate one that might be your best option since I noticed that the air seal is completely dependent on the recessed 0-ring inside the cap and would be difficult to duplicate with a generic cap. Hmmm, maybe I should donate mine to my creepy neighbor who always want's to borrow my bike tools before it fails on me.