most common types used are 250k, 500k, and 1M (thats 1000k)
these numbers represent resistance at max, so when used as a volume control, this represents resistance to ground at max. obviously, resistance will double on a strat if you use 500ks, and quadruple with 1M's. Due to the way pickups work, not only does this increase volume, but frequency range as well, in the treble range. So this will increase treble, and change the 'shape' of the top end. However, in a strat style volume control, all that changes when you turn the pot down is resistance to ground. So a 500k or 1M pot can be turned down to have a 250k resistance to ground, so you are losing nothing by changing to 1M.
The reason it seems like your pots have no range is most likely because they are not logarithmic. A non-log 1M pot used as a volume control, and turned down halfway will have a resistance of 500k, but our ears would hear that as being much louder than half of full volume. A logarithmic pot compensates for this, so that a 1M at half has 100k resistance, which is what our ears hear as half volume when its used as a volume control. Don't order pots from guitar stores, order from electronics stores.
Http://www.smallbearelec.com/StoreFront.bok
