44 to the base 30 a v notch 38 is placed in top surface 36 of support block 32 to receive a connector 28 a clamp 48 see fig6 has a hoop shaped body 50 terminating in inturned ribs 52 which are free to move along the recesses 40 of the support block 32 centrally positioned in body 50 is a threaded aperture not visible into which is threadably engaged a threaded rod 54 the end 56 of threaded rod 54 can be brought into contact with a connector 28 in v notch 38 by rotation of the rod 54 employing the knurled head 58 with a connector 28 in v notch 38 the movement of end 56 of rod 54 into engagement with such connector 28 also causes the inturned ribs 52 of clamp 48 to engage the top surfaces defining recesses 40 and thus lock the clamp 48 to the support block 32 and the connector 28 to the support block 32 similarly the retraction of end 56 of rod 54 from connector 28 permits the removal of the connector 28 and the clamp 48 from the support block 32 a drive rod 60 see fig7 passes through an aperture 42 in support block 32 to an annular collar 62 adjustably affixed to drive rod 60 by a suitable fastener as will be described below the drive rod 60 is moved in the direction of arrow 64 in fig2 until the annular collar 62 engages rear surface 39 of support block 32 and any further movement in such direction causes support block.