On Wednesday, August 21, 2019 at 2:13:36 PM UTC-7, AMuzi wrote:
This is a USAF spec internal wrenching bolt:
https://www.skygeek.com/military-sta...rilled-hd.html

Here's a DIN912 cap screw:
https://4.imimg.com/data4/SG/TV/MY-2...ws-500x500.jpg

or smooth side version:
https://img.accu.co.uk/products/SSCF-A2_lg.jpg

Tom has a point in that most linear ("V") brake anchors do
not have cylindrical heads and actually do look more like an
'internal wrenching bolt':

https://i5.walmartimages.com/asr/9e1...0&odnBg=FFFFFF

p.s.
A metric DIN #912 cap screw is usually under a dollar. Not
so with Actual Bicycle Parts!

https://www.walmart.com/ip/Tektro-An... 34&tmode=0000


BTW, that internal wrenching bolt profile is used for Hollowtech pinch bolts. https://images.amain.com/images/larg....jpg?width=475 It leaves little material near the top, and if the wrench is not seated, it is easy to wallow out the fitting. A standard M6 hex cap screw gives you more material to support the wrench, but its a tight fit in the arm.

-- Jay Beattie.