This is a replacement male push buckle typical of that found on backpack waist straps. This was designed as a replacement and is compatible with an off-the-shelf female part. The buckle will suit an aperture 41mm x 8.4mm. Check the dimensioned drawing provided for an overall indication of size.
The Fusion 360 archive is also provided if you need to tweak the design to suit a different sized buckle.
Blog post: http://www.samjohnston.net/blog/male-push-buckle-replacement
This should be printed flat for the greatest strength. Supports touching the build plate are required. Print this at 0.1mm for a nicer finish.