This is not a "Pro" job neither a tutorial, only two simple attempts cause I couldn't find these leathers cups size. I asked for a piece of leather to local shoemaker. I realize is to much soft... but good enought. I soak a leahter cutout in water for 20 minutes before using. First attempt: For an old brass hand pump I need a 22mm diameter cup. First FOCUS stoves had not a built-in pump. I drilled a hole in a wooden board. First with a 20mm Diamter drill. Then with a 22mm D drill only HALF DEEP. With a sandpaper I got a tappered bore. I cut a 20mm D wooden stick and sand a conic shape in one end. Both was varnished. I pressed the leather with a clamp for one night. Voilà! I cut the extra leather behind the board with a cuter. It isn't a good idea... I made a hole. I assembled the new leather cup. Leather cup spend one night soak in oil. Second attemp: A 34mm diameter leahter cup for a fuel tank pump. I drilled a 32mm Diameter hole and tappered a little with a sandpaper. You can see the conic end of the stick. Wet leather is so soft you can shape it with your fingers! Soaked leather is darker than dry... In this case I cut the waste with a scissors. These are the pump parts. You can see the old cracked cup. I assembled the new cup. One night soak in oil. The extra oil drops for a long time. This is the result I reach 2kg/cm2. It's good enough for me!!!