Fein KBH 25 Repair Manual page 30

Fix drill shaft in gearbox housing with circlip
Rotate drill shaft until the wrench flat provides good access for inserting the circlip
Attach ring, insert balls, fit pressure spring
Attach sleeve and press down
Attach disc and insert circlip
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FEIN REPAIR TOOLS
5.2. Fitting the gearbox
C-SC_CSSM 2012.05
Tool:
- External circlip pliers
- Longsleeve Circlip, angled