Rail (625Wh) you may want to watch this #TREKRAIL

Wilbur

Member
Dec 12, 2022
118
84
New Zealand
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.
  • 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
This is what I'm thinking would work:

Class 12.9 non-serrated:
McMaster-Carr


1683687580140.png


Or Class 8-10 serrated :
McMaster-Carr
1683690323452.png
 
Last edited:

Stihldog

Handheld Power Tool
Subscriber
Jun 10, 2020
2,894
4,079
Coquitlam, BC
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.
  • 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) than the original heads so I need to check frame clearance
This is what I'm thinking would work:

Class 12.9 non-serrated:
McMaster-Carr


View attachment 114164

Or Class 8-10 serrated :
McMaster-Carr
View attachment 114170
I wonder if those heads might be too tall for clearance’s in the motor compartment?
 

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