Clamping bar secures master fixtgure to tube. M6-10 for 3" to 6" tube. Indexing bar locates master fixture laterally on tube. Indexing bar shims 4 each end 1/16" thick allow back-set adjustment. Indexing slot locates master fixture longitudinally on tube and insures proper location of router drill jic template. Precision machined resting pads allow master fixture to be used with fin tubing and insures parallel alignment of jig with tube surface. Three tapped holes at each end of master fixture for easy attachment of over 100 router drill jig templates. One hole at each end of master fixture for mounting 2 or more fixtures on seven foot bar for more than one cut-out. Large thumb screw insures positive clamping of master fixture to tube. Heavy-duty weleded construction. All parts plated or enameled. Machined surfaces and precision assembly of master fixture ensure accurate cut-outs with all router drill jig templates.