Sure, it's simple, but it's functional and cheap! This lock stem probably fits about a 100 different vehicle models, but I designed this one for a friend whose lock stem broke off of her 2008 Pontiac Grand Prix.

Print instructions

Printer Brand: Prusa
Printer: I3 MK3S
Rafts: Yes
Supports: No
Resolution: 0.1 mm
Infill: n/a
Filament: Prusament PETG Black
Notes:

PETG or ABS will ensure that it doesn't melt in the hot sun. Choose enough perimeters so that infill becomes a non-issue. Raft helps to keep it from falling over during printing. When printed with the parameters above on an i3MK3, the hole is just small enough to provide some resistance and thread itself. If yours comes out too tight, you can waste 5 cents worth of plastic and reprint slightly bigger, or try heating up a long bolt with the same threads as your lock shaft and thread it with the hot bolt.