elements protruding above the work surfaces 36 37 and in alignment with a travel screw 48 49 the travel screws 48 49 extend through openings through the stationery clamp elements 50 51 such as opening 52 and movable clamp elements 54 55 are positioned in sliding relationship on parallel legs 40 41 and 42 43 with each movable clamp element defining an internally threaded opening therethrough such as opening 56 of clamp element 54 the external surface of travel screw 48 is formed with a helical thread extending thereabout which engages the threads of openings 56 of each movable clamp element 54 55 so that when each travel screw is rotated its movable clamp element 54 55 moves toward or away from the stationery clamp element 50 51 the travel screws 48 49 can be rotated manually by rotating the handles 58 or 59 that are connected to the outer ends of the travel screws clamp level arms 60 61 are each pivotally mounted intermediate their ends by pivot pins 62 63 to mounting plate 24 the clamp lever arms are oriented approximately at a right angle with respect to each other with their inner ends each including a cleat 64 65 with each.