They have the same action (i.e. a curb or leverage action on the bars, chin groove and poll), but with the pelham there is the addition of a second set of reins which, when used, cause the bit to also act on the bars and corners of the mouth like a straight bar snaffle. The weymouth is not often used alone, it is traditionally used in conjunction with the bradoon, or small ringed snaffle, in which case they are together called a double bridle and each bit is used independently with separate actions.