OP
As in a second bolt snap for Al cylinders or something else?
To be clear the below examples work for me with 2x cylinders for recreational diving
When I'm donning my cylinders I will use the top bolt snap to suspend the cylinder and stand up, then Ill connect the lower bolt snap. Once in the water Ill remove the top bolt snap and wrap the bungee around the valve. This keeps the cylinders nice and tidy for me.
When I'm on a boat I will attach the top bolt snap, and leave the lower bolt snap unclipped. This allows the cylinders to hang in front of my body (not at my sides, so I'm not wider than normal). I typically do not enter the water with my mask on (its bolt snapped to my bcd), this allows me to hold onto each cylinder as I enter the water. Once in the water I will connect the lower bolt snap, remove the upper bolt snap, and wrap the bungees around the valve.
Using the above process I am able to get into the water a bit quicker than my recreational backmount buddies and I'm usually ready to go when they are.