None of the existing servo brackets on Thingiverse quite met my needs so I made my own.

Fits standard size servos with enough room to fit the cable through even allowing for ABS shrinkage and is thick enough for more heavy duty applications. I had issues previously with the center hole being too tight lengthwise, so moved the mounting holes apart slightly. It should still fit most standard size servos.

See https://droidbot07.blogspot.com/search/label/Stewart%20Platform for more.