Harland Sharp is in stock at Summit and may or may not come with bolts. But was going Studs Description states steel but later on says aluminium. So wonder what they are.
The HS BB hold downs I bought recently are steel. But I did see that "aluminum" description as well. Bolts were not included. I bought Gr 8s after measuring for bolt thread engagement I wanted. Stout parts IMO.
BTW, while checking different sources I also saw some complaints for some of the SB purchases indicating they were sent hold downs for 3/8" bolts. HS might be just a phone call away.