35,6x57x3mm
A keyring, a small chain or a carabiner
I printet it our of TPU with the 0,2mm quality setting (3 perimeter and 15% infill) an it tourned out perfect. In my case, no post-processing was required. Of course you can also give PLA or PETG a try but I thought TPU was the best because ist will not crack in the pocket.
The hart shaped hole is for additional fixing (sew on) of the knitted sock.