This is a loop for a Swatch watch strap, but it's quite generic and would probably fit other watches. There are two versions: loop1 has internal dimensions of 17x3.5mm and 1.2mm wall thickness, and loop2 has internal dimensions of 17x3.4mm and 0.8mm wall thickness.
In my case, I used the second version with thinner 0.8mm walls.
To fit the loop, I used a metal pin to push out the strap retaining pin, removed the strap, fitted the loop then reassembled.
Ancubic Kossel Linear Delta
0.2mm layers, 0.8mm shell thickness
Printed in rigid.ink transparent PLA at 195C nozzle and 50C bed, came out great.