When you install one of these glass filled engine mounts, your model will be lighter and your engine will have a much better chance of surviving in the case of a mishap. You see, these mounts are designed to take the shock of a severe crash or mishap and break away, protecting your engine. A metal engine mount is just as strong or stronger than the engine so the engine runs a much higher chance of breaking. Size Range 1.080-1.180 in. Typical Engine ASP .25, Brat .21, .25, .28, Enya .19, K&B .25, O.S. .21, .25, .28, Royal .25, Thundertiger .25