This is a Glock / Square Compensator made by me. I have not tried it on a SSP18 but a SSE18 works perfectly.
It's screwed on a 14mm counter clockwise thread and tightened by a clamp like mechanism to hold it in place. It has cutouts on top so it might work on a Gas Blowback Pistol as a compensator but for the SSE18 it has no function besides the beauty factor :)
Print it with the thread facing downwards to the printing bed.
I'd recommend printing it with 100% infill as I did because it's meant for use on an Airsoft field. But feel free to scale down the infill.
Compensator_v4.stl | 488.7KB |