The 
SKIL 2610968747
 is an official OEM Retaining Ring (also known as a spring retaining ring or circlip) used primarily in Skilsaw worm drive circular saws

Compatibility
This part is compatible with several major Skilsaw and Bosch circular saw models, including:
  • SKIL: HD77 (Types 14, 15, 16, 17), SHD77, SHD77-02, MAG77LT, and HD77M.
  • Bosch: 1677M worm drive saws