These are hammer bolts designed for 1515 aluminum extrusion (1.5" by 1.5", not 15cm by 15cm), though they'll probably work in other T-track types, too.  They're ¼"-20 threaded.  There are three lengths: 20mm, 30mm, and 40mm (so, roughly, ¾", 1-1/8", and 1-½").  

Here's the thing: they work, but it's not pretty.  Print them lying on their sides, and you'll need to support them from the print bed.  You'll need to clean the threads up with a die (¼"-20; go easy).  It's kind of a pain in the neck, to be honest.

I've tested and printed these in PETG, with 50% infill and four perimeters.  I'm sure other filament would work fine, but you're on your own there.

Just to state the obvious: plastic is not as strong as metal.  These are not as strong as metal hammer bolts.  Do not try to use them in ways which require that they carry significant load; they will fail.  Even if you use whatever the fanciest latest carbon blah blah blah.  These are for light duty applications only.