On my double I have the flip up "night" sight and the thing just couldn't flip up on its own, or down on its own either. The regular standing bead is essentially the same as the catapillar sight 500grs posted. The flip up used to come in two heights and one bead size but according to NECG you can only get one height now as 500 noted.

FWIW they suggested filing the brass bead at a 45* angle, lower point toward action, higher toward muzzles, for increased visibility with any size bead. I tried it on my 375 and it worked. In the end I went with the "fiber optic" sight like 500 posted in the midle "bead" size for my 375 and it is really visible against any color target, more visible than the much larger night bead of the flip up on my double. I'm not sure of the robustness of the fiber optic sight so I replaced the solid hood the 375 came with with one from NECG which has oval holes on each side to let more light in. This really works too.

Back to the flip up sight, it is much more visible than just the brass bead, especially if the bead is not filed at 45* and polished. I think it would be useful in thick brush and toward dusk. It shoots to the sme poi at 25 and 50 as the brass bead so far as I can tell. It subtends (?) about six or eight inches at 50yds. I will report how it works on my safari which is coming up soon.

JPK