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Look closer, it polished aluminum. I am unaware of a scuba tank made out of stainless.\
So that is why your tanks is SS
Sorry I could not resist.....
As for the butterfly snap, I do not use them because the the added area acts as a guide or funnel if anything gets in it. A line can get stuck in that area and pulled right through the gate of the bolt snap.
The whole "Don't use Brass because it will cut you" is a load of crap IMO.
I never heard of anybody having a problem or mentioned anything about that until DIR came on the scene and made it one of their OCD policies.
Divers have been using brass since diving began.
The spring is exactly the same as a stainless snap - their both stainless springs (302)
Brass is available and relatively inexpensive.
Don't buy silver shiny chrome plated steel at Home Depot or your local ordinary hardware store thinking it's stainless because it's not. Those will rust out.
If you're worried about a brass barrel guide cutting you then all you have to do is take a ulitity knife and shave the two edges of the channel down so they are bevelled and the edge rounded down. It takes about five seconds.
Brass is plenty strong too, you're not hoisting engine blocks after all.
I've checked all the brass bolt snaps I have used for years and there is no sign of sharpening on any of them.
If they get salt corrosion then lube them up. Brass is a nautical metal.
Stainless is a prestige thing, it looks cool, that's it.
The top snap shown by the OP not only is a hazard because unwanted things can get clipped on it, but a line loop can also come back around on it and open it and you will lose whatever it was you had clipped off.
I've had fishing line catch the button on a regular bolt snap, as where on the snap with the spike sticking out fishing line may hang up on it but will also slide off easily.