These steel prop adapter nuts include prop washers and are also CNC machined to offer the best possible quality. They are available in different crankshaft threads to fit many engines on the market. To avoid the problem of long screws, which tend to flex and break at the point where they enter the adapter nut, we make 4 lengths of adapter nuts: Short, Long, X-Long and XX- Long. This allows for the use of shorter screws, which don"t flex and break. Although it will depend on the thickness of your prop and the spinner size, as a general rule, always use the longest adapter nut possible. Use SHORT adapters with spinners 2 1/2?? and under. Use LONG adapters with 2 3/4?? to 3?? spinners. Use X-LONG adapters with 3 1/4?? to 4" spinners. Use XX-LONG adapters with spinners 4 1/2" and up. Use a LOCK NUT with an adapter nut on 4-stroke engines. If you are using a LOCK NUT, you need an adapter one size shorter. If you are selecting an adapter nut for an ULTIMATE spinner, which is over 2 3/4" in Dia, pick an adapter one length longer. If the Ultimate spinner is larger than 3 1/2 in Dia, use an XXL adapter.Dave BrownPart DAV9710