This is a Duel Magazine Holder for S&W 4506 Mags.
I made this just for shooting competitions so I'm not sure if it would be suitable/comfortable for everyday carry.
The retention spring is secured with a 6/32" Heat-set Insert and a 6/32" x 1/2" Screw.
I'm still playing around with the infill used on the retention spring for proper tension as it might weaken over time but I printed everything in PETG at 80% infill for durability so I'll have to see how long it last.
The holder may fit other .45 mags... for reference the S&W mags this was designed for measure roughly 1.37" x .55". The belt loop holes are 1.65" x .25" so they should fit a wide variety of belts.