Reading the add in this one say's stamped steel -
https://www.classicindustries.com/pr...s/CT26720.html
The Truck Shop shows the back of them here, doesnt "look" brass but I'd call and ask.
https://www.ebay.com/itm/12411993381...=&toolid=10050
Ya I find it a dubious statement that they're brass but maybe they're out there selling them someplace like that.

Brothers say's theirs is steel also -
https://www.brotherstrucks.com/1964-...tinfo/HCC5C66/