These will really help seal up the build space when printing ABS/ The covers swivel to allow them to be closed with printing ABS, and open when printing PLA. They don't need to be removed and snap into place. They fit very nice.Do not scale. Once both pieces are printed flex the flapper to help it go into the swivel holes. If you push hard enough they will snap it. Its easier to just flex the flapper a little. The flapper needs to spin a few times before it spins easily. I printed them in PLA Both pieces take about 90 total and I used 7% fill.