How is that penis cap called - from vintage porn mags

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I remember when I was young I saw some vintage porn magazines and some men had some sort of a penis cap that only covered the head of the penis, either black or white.

How is it called and what is it for?

I tried to find it myself on google, but I failed.

[hpjf]

it's called a rolled-on condom

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No it was thick, like a silicone cap, didn't look like something that could be rolled.

[hopless3]

I remember seeing them ( God I'm showing my age ) But I don't remember them having a special name