Our newest holder uses a 3/8 316 stainless steel swivel bolt snap with split ring on one end of the holder and a high retention force plastic clip on the other end.
You can clip off to d-rings, use them to hold your smb in place by securing from the smb to d-ring on your rig
We found many uses for these holders and even hold your gloves or mask when getting into or coming out of the water