Well, I put those characters into DuckDuckGo, and the translation didn't make any sense.
Sometimes, an equivalent or analog expression is better for the intended audience than a direct translation.
The third character is wrong (they do look similar)
(肛精铢股 -> 肛精鉄股)
It's almost pronounced the same way as "鋼筋鐵骨"(traditional characters) or "钢筋铁骨"(simplified characters)
which literally means "tendons of steel, bones of iron"
It's used to describe someone who has a strong/sturdy body
The author changed the characters so the individual characters are somewhat related to the crotch (to make a bad pun)
肛 = anus
精 means sperm in the word 精子
鉄 means iron (this was not changed)
股 is part of a character in the word ass (屁股)
I think TL did a good job translating it 👍