gezer2u is talking about the CRC mounts.
The problem is that if the servo twists it will loosen one of the mounts, and if it twists in the other way it will loosen the other mount. So you end up with a servo that can twist a little in either direction.
I suppose you could use locktite or something to prevent this, but I would just avoid them all together.
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My recommendation is take the money that you would have spent on an adapter plate, and spend it on a carbide 3mm drill bit. Then use that bit to drill you a new hole in your chassis. Carbide bits dont dull like regular drill bits so it will probably last you a practical life time. 3mm is good for 4-40 through holes.
Really it shouldnt be hard if you only have to drill a single hole in the chassis. Just measure, and use a SMALL drill bit to create a little divot, and then use your carbide bit.