Antique: I just looked at the back-side of my Echo 2400engine. Around the crank seal you will see a perfect round part of the case around the seal. The O.D. is about 1.010 inch DIA. Now if the right size hole is made in sensor mounting plate...it will press on to that. A little locktite and it will stay. There is one web at top on my engine that would need to be removed. I think you will see what I mean. Capt,n