1966 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-33 -- Roll Bars

a. Steel roll-over bars are compulsory, and must be approved by NASCAR. Front and rear roll bars must be connected at top (cage type) and bottom on both sides at seat height. Side roll bars are compulsory and must extend into door panels. Aluminum and other sofe [sic] metals not permitted.

b. Roll bars must be welded, and must be not less than 1 3/4 inches in outside diameter and walls must not be less than .090 inch thick. All welds must have gusset plates, and no less than .090 steel. No pipe fittings allowed.

c. Roll bars must be padded and taped with foam rubber from bottom of left window to center of top in all divisions.

d. For recommended method of installation of roll bars, see diagrams on rear pages of Rule Book. Note for AeroWarriors.com users - there are three diagrams: here, here and here.