Wilbur
Member
So I've done a little research on replacement M5 screws for Gen 1-3 Bosch motors. The originals are black M5 x 16mm flanged security head (T25 5-pt pentalobe). The 11mm flange is not serrated. The head is ~3mm tall. They don't appear to be thread-forming as the tip isn't blunt-tapered, (even so, Bosch recommend not removing the screw completely when tensioning/resetting in order to preserve the threaded aluminium material). The coating appears to be black oxide or maybe zinc.
Ideally I'd like to replace them with a M5 x 16mm flanged and serrated class 12.9 cap screw.
Class 12.9 non-serrated:
McMaster-Carr
Or Class 8-10 serrated :
McMaster-Carr
Ideally I'd like to replace them with a M5 x 16mm flanged and serrated class 12.9 cap screw.
- Flange is important as it spreads the load on the aluminium brackets.
- Serration would be good to improve screw grip in the presence of vibration.
- Class 12.9 is the highest tensile strength alloy steel available (170,000 psi) and a cap screw can have a 4mm allen socket, instead of the annoying pentalobe head.
- Flanged cap screws are a little taller (5mm vs 3mm) than the original heads so I need to check frame clearance
Class 12.9 non-serrated:
McMaster-Carr
Or Class 8-10 serrated :
McMaster-Carr
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