Some quick draws have o-rings or such to stop the 'biner from turning the wrong way in the sling which seems like a good idea, but then some dont at all (I suppose this makes them lighter but mostly cheaper?) then just to confuse things some quick draws have an o-ring on only one of the two 'biners (so that only one 'biner is free to turn around in the sling) what is the logic?

Mostly only the bent-gate (or biner that will be clipped into the rope) have these 'o-rings' or 'Strings' (what Petzl call them).
The reason that your straight gate biner (the one you will clip into the bolt) is normally not fastened is because it generally does not turn upside down as it is weighted by the lower biner while hanging on your gear loop. I'm sure price does come into it, but it’s also convenient to be able to break up your quick draw for many reasons. For Trad climbing is one reason.
Primarily though, if you've dogged up a route but would like to make a Red point attempt, you pull the rope down (leaving your quickdraws on the route). If your rope clipping biners (bent gates) are not fastened with a String (or other) there is a good chance your bent gate may turn, making clips a little trickier while holding the crux crimps during your Red point attempt.
Should the biner clipped into the bolt turn, no big deal as you can easily get to it while being lowered off the route.
The Petzl Strings weigh 2 grams each.

Just don’t do this with your quickdraw

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Climb ZA - Administrator

Hi Justin, Thanks for the detailed answer, I bought a set of fader fly's (they have no \"strings\") and I have had a situation were I was battling to clip the rope in (the bent gate had turned) while I was slipping off a cr#@py grip. so my draws are going to get lots of strings

Petzl Strings R7.20 for 1. I think the O-ring's would be a little cheaper

Elastic bands and rubber O-rings found at your local hardware store will work too

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\"If you don't break your ropes while you're alive do you think ghosts will do it after?\" -
Kabir

You should NOT put o-rings on both ends of a quickdraw. The reason is that a normal quickdraw is quite stiff (the webbing) and if you secure BOTH biners then the whole thing becomes stiff. This means that the rope could twist the whole draw and the gate of the biner on the bolt could end being loaded against the hanger (most biners will break in this case), alternatively the biner can unclip from the hanger.

This is exactly the reason why you don't put a single biner on a hanger and clip the rope in - it can EASILY unclip itself.

Long slings don't matter because the webbing is flexible.

The same thing applies if you want to extend a draw. NEVER clip two biners together. Rather remove the top biner from the one draw (this is easy because it is the one without the 0-ring) and then attach this to the bottom biner of the other draw.

most of the issues raised in the other postings are addressed by the Black Diamond express slings which include the \"straight jacket\" feature - a rubber insert positioned inside the webbing loop which really holds the botton (rope clipping 'biner) very tight. The upper loop is left quite loose, which is very helpful in trad climbing in particular, when one wants to link two draws together - one just inserts the bottom 'biner of one 'draw into the top loop of the second draw. This gives a quick & very safe double length 'draw.

The main reason for only the one rubber securing thing (whatever you use) is as Guy describes. Creating a stiff inflexible join at the top biner can be hazardous to your health! This joint must be loose and flexible, otherwise the top biner can 'hang up' on the bolt hanger and sit in a twisted position causing it to unclip itself or even break in the event of a fall.

O-rings last longer than rubber bands and are available from engineering shops or rubber prodct suppliers. Another excellent solution are pig castration bands ( !, wickedly strong tiny rubber o-rings), ask a pig farmer or check agricultural supply stores. Put one of these on your pinky (not easy) and pity the poor piglet!!