So I have read that impact sockets are generally made of Chrome Molybdenum and are supposed to be a little softer so they can absorb the impact of an impact gun, whilst Chrome sockets are harder and cannot absorb sudden increases in torque.
So this gets me wondering if it is actually valid to use impact sockets with a hand torque wrench? Would they flex under torque slightly an skew the torque applied?
Short answer : no, you can't apply the force suddenly enough to make the socket flex to make a difference - what can skew the readings or, at least, the torque applied is friction between the nut or bolt head and the surface it is mating to. That is why some manuals state the type of lubricant to be used between the nut / washer etc.
Impact sockets are exactly as you describe them (This Ingersoll Rand Tool Tip provides info.)
Don't let the idea of the impact socket being more pliable fool you. The main idea of the impact socket and the reason why it can flex is to handle the extreme, sudden torque which is applied through the impact gun. This flexibility will not affect the outcome of the torque which is being applied and measured by the torque wrench. The reason for this is because if the socket head flexes during the torque, the torque wrench doesn't register the give (it equates it to the same amount). Since the socket is attached to the head of the torque wrench, it's considered part of the torque wrench (the head of the fastener could be considered the same). You may twist the handle more, but the needle won't swing any further (or the click won't happen or the meter won't register any more torque applied).
The flexing of the socket is so minimal, this should never be a worry. For that matter, a regular socket is going to flex as well, but we don't worry about them. It will just flex a little less than an impact socket, is all. Again, the difference is going to be quite minimal and nothing to worry about.
