Front part is an arch (that it's put on, the hemisphere type) and has a hole in an upper part more slightly than a center, so from here, only a penis, it seems to take it out, it'll be.
A diameter in a hole extend up to about 4 centimeters for 2.5 centimeters, so even a thick penis is OK from attenuation.
KH377 Holey porch G-strings
MEN'S UNDERWEAR SIXLINES TOKYO JAPAN