pop in
(to something) 1. Lit. Inf. to come or go into some place, such as a store, shop, etc., for a moment. Let me pop into the bakery for a minute. I have to pop into the drugstore for some shampoo.
2. Fig. to snap into place in something. The little plastic thing popped into its slot, and the model plane was finished. It pops in and holds tight if you do it right.