A simple friction fit clip-on for the NERF Alpha Trooper (all versions except for the accutrooper) that is inspired by the SIG 552 you may know from Counter-Strike or Airsoft or something. The barrel is fake and in my case 16mm x 5cm (tell me standard imperial tube dimensions and I can make a US version). In the fake barrel there is space for an M3 screw you can secure with a 20mm (3/4") washer in the blaster to make it more stable.
Also check out my SIG-Style Diopter sights!