I purchased this when the original cap from the Oster Pro 1200 broke after only a few months of occasional use. I considered tossing the whole blender because that’s the second Oster where this piece keeps cracking in spite of never having seen the inside of my dishwasher. It also “stuck” in the base with every use and was a pain to remove.I decided to try this jar bottom cap as a last chance for the blender to make me happy and I am very glad I did! Not only does it fit the glass jar perfectly without leaking (provided you put the gasket into place properly and tighten it snugly). The best thing is that if fixed my main annoyance with the original cap that was so snug in the base that I had to wrench it out after wiggling and lifting. I guess that stress contributed to the early demise of the original cap.This replacement cap seems to be a teeny tiny bit smaller on the outside so the jar slips into the blender base smoothly and can be lifted out just as easily without stressing the plastic. I’m very happy with this now and will purchase one as backup, just in case. And the blender is allowed to stay.