. . . "In the clamping position it will be seen that the clamp 20 assumes a lar'ge' ly oblate or elliptical shape as the two segments 25 and 26 pivot towards each other about the inner edge of segment 24, which edge may be provided with slightly enlarged cutout portion 29 to facilitate this operation. a The clamps 20 may be formed, for example, of a metal such as vitalium or other metals found safe for u" . . .