Question about Hentai (in manga) censorship

I noticed that in some Hentai mangas, there is a black line which covers a part of the penis between the glans and the body.
My question is: Why is that part being covered?

Tradition.

because japanese people know that they can't fap too black bars going in and out so they atleast let some of it show. there a good people

Because Japanese censorship laws.

Because of silly japanese censorship laws, instead of turning a penis into a black bar or pixels they cheat by just drawing a black bar over the part you mentioned since then it still counts as censorship but still shows plenty.

Badly written laws. /thread

>>5
wouldn't that be good for the read/see'er?