Use PETG for durability and it will last far longer than a bought one. The flat spot on the rim is so it will fit on my MK3. Fair warning: 1) It takes a good bit of filament to print. 2) It's a slow print. 3) You will have to waste filament on support. I print it right side up and support the outer rim only. My first one has lasted 2+ years. The washer and nut are replacements for the ones that used to hold my skimmer basket on.