Is that really true?
Nobody really knows, doggone it. There’s not even very many references to crucifixion in surviving records, and no "how to" manuals at all. Everything posted here, written or pictorial, is purely speculative.
One of the most plausible fictional treatments of 1st century crucifixion I’ve ever read is in a 1968 novel by Frank Yerby.
https://en.m.wikipedia.org/wiki/Judas,_My_Brother
Told from the first person point of view of a Romanized Jew who’s a boyhood friend of Jesus, the narrator recounts his own crucifixion at the hands of drunken legionaries. They tie him to an X cross, and intend for him to die. He does suffer atrociously, but is rescued and recovers. And he notes that this is the standard practice for crucifixion.
He’s later present at the Crucifixion, and thinks to himself, "My God, are they nailing him to that thing?"
The book's a kick-ass good read. And it’s informed speculation. But it’s still just speculation. For my own twisted fantasies, I’ll stick with nails.