Hidden AirTag mount under bike saddle rails
A small clamshell that bolts between the two 7 mm rails under a bicycle saddle and hides an Apple AirTag (31.9 mm diameter, 8 mm thick) where a thief will not look. The AirTag pocket is 32.3 mm across and 8.4 mm deep, the lid closes with two M3 screws into heat-set inserts, and the rail grooves are spaced 44 mm apart, the common centre distance on road and mountain saddles. Walls are 2.5 mm, the speaker face is left slightly open so alerts still sound, and both halves print flat.
Saddle rails and pocket depth both need to be exact for the mount to stay silent over bumps, which a generic download cannot promise. In SpeakCAD you measure your rail spacing and diameter, preview the mount free in the browser, tweak the clearance in the chat, then download the STL and print it in black PETG.
Create a two-part AirTag holder that clamps to two 7 mm saddle rails spaced 44 mm apart, with a 32.3 mm diameter, 8.4 mm deep pocket, two M3 screw holes for heat-set inserts, 2.5 mm walls, a 12 mm speaker opening and 0.3 mm rail clearance.