If you had a TryAll rim with 32 holes and 3 cross pattern your spokes are 262 and 261, or at least they should be. Im not sure if spokes comes in diffrens of 1mm. I think its 260mm, 262mm, 264mm and so on. If you need 257mm allways go for the longer one, in this case 258mm. Anyway thats what I think and was told when I learned to build wheels.