My Steelseries Apex keyboard recently lost one of its rear feet during a move, and Steelseries support doesn't sell or provide replacements.  This is a model for a replacement foot that roughly matches the stock foot – it's not an exact reproduction, but the external dimensions are the same to within 1/32" and the replacement fits snugly in the existing slot without excess force.

This part is known to be compatible with:

• Apex 7
• Apex Pro

This part should be compatible with other Steelseries Apex keyboards as well, including

• Apex 3 and 3 TKL
• Apex 5
• Apex 9 TKL and 9 mini

(Please let me know if it isn't!)

Any rigid material is fine.  ABS, PETG and PLA+ are ideal, but I used plain PLA and the arms still comfortably bent enough to fit the pegs in.  The pegs need some minimal supports, and I recommend a very small layer thickness to smooth out the sloped top surface.

The stock feet have a slightly rubberized surface on the tips.  If this is something you need, dip the feet in Plastikote or a similar tacky surface preparation.