Garmin Edge 840 out-front mount for 31.8 mm bars
An out-front mount that clamps a 31.8 mm road handlebar and holds a Garmin Edge 840 (or the identically sized Edge 540) level with the stem, roughly 75 mm ahead of the bar centre. The quarter-turn socket copies Garmin's four-tab pattern so the unit locks with the same click as the original, and a 1 mm recess under the head keeps the 57.8 x 85.1 mm computer clear of the arm. Two M5 bolts pinch the split clamp, the arm is 8 mm thick with a rib underneath, and it prints upside down on the head face in PETG for vibration resistance.
A generic downloaded mount always compromises somewhere: the wrong clamp size, an arm that is too long for a short stem, or a socket that rattles. In SpeakCAD you type the clamp diameter, reach and drop you want, preview the mount free in the browser, refine the arm shape in the chat, then download the STL.
Design an out-front bike computer mount with a split 31.8 mm handlebar clamp closed by two M5 bolts, an 8 mm thick arm reaching 75 mm forward, and a Garmin quarter-turn socket with four tabs, 1 mm clearance under the head and 3 mm walls.