Picture #2 shows bevel on tooth that must face starter. Picture #3 shows bevel in bore which goes toward flywheel. To shrink fit; Clean mating surfaces. Lightly oil machined surface of flywheel. Cool flywheel in freezer or soak in ice water. Warm ring gear with torch, oven or grill to 300F to 350F. You are going to need good oven mitts or welding gloves to handle the hot ring gear. Have a hammer and block ready in case parts stick. There are some good videos to watch online. Always check for loose magnets before installation. Thickness is about 3/8".