15 to 12 mm thru-axle skewer insert
thingiverse
Endplugs for transitioning from 15 to 12 mm through axle skewers. Not suitable for 3D printing. Turn it on a lathe instead. Drawing in inch and millimeter measurements. I listed the closest American/imperial drills for the 12 mm bore. Then, I used a boring bar to turn the ID exactly to 12 mm. In practice, the 15/32" drill bit worked perfectly to start the hole. If you're feeling fancy, you can add O-rings like this (https://www.ebay.com/itm/J-L-15mm-12mm-Thru-Axle-Hub-Conversion-Adapter-FOR-Hope-Mavic-DT-Swiss-Shimano/201740754770?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20140131123730%26meid%3D16dcab470e5344fcb2190f7d817f83b8%26pid%3D100167%26rk%3D5%26rkt%3D15%26mehot%3Dlo%26sd%3D272908309994&_trksid=p5411.c100167.m2940) to have some measure of retention in the hub. In practice, with my Shutter Precision/Exposure PD-8X hub, the fit was loose, so I could definitely see these getting lost if you're changing a flat on the side of a road without O-rings.
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