A mandrel suitable for forming a hollow part from a heat curable material includes an (a) an elongate central member having a coefficient of expansion which is different than the coefficient of expansion of the cured heat curable material, (b) at least one lateral member disposed at a first location and projecting away from the outer surface of the central member, the lateral member being slidably attached to the central member, and (c) a rigid elongate strut member having a coefficient of expansion substantially similar to the coefficient of expansion of the cured heat curable material. The first end of the strut member is affixed to the lateral member, and the second end of the strut member is affixed spaced apart from the lateral member.