This is the Case Set for the Hitec HS-50 sub micro servo (HRCM0985).
Clear blue plastic construction
(1) Top, center, and bottom case sections for the Hitec HS-50 servo
Transferring all components from old case to new one.
Length: 0.82" (21mm)
Width: 0.47" (12mm)
Height: 0.90" (23mm)
Also available in black - HRCM6354.