Even though Martin lists their linbs in 10 lb increments, they are available in 5 lb increments. Martin makes all their limbs themselves, then tests and matches them, except in the case of the XRG limbs which are manufactured by Martin as a pair from a single stock. My Altitudes are rated at 65lbs, and my MV2 is rated at 55lbs. But a 55lb limb may actually be 57, but not 53. Having a matched pair is the key. I better shut up now because I have pretty much spewed everthing I know about limbs at this point...lol.