Section 1512.4 - Mechanical requirements(a)Assembly. Bicycles shall be manufactured such that mechanical skills required of the consumer for assembly shall not exceed those possessed by an adult of normal intelligence and ability.(b)Sharp edges. There shall be no unfinished sheared metal edges or other sharp parts on assembled bicycles that are, or may be, exposed to hands or legs; sheared metal edges that are not rolled shall be finished so as to remove any feathering of edges, or any burrs or spurs caused during the shearing process.(c)Integrity. There shall be no visible fracture of the frame or of any steering, wheel, pedal, crank, or brake system component resulting from testing in accordance with: The handbrake loading and performance test, § 1512.18(d) ; the foot brake force and performance test, § 1512.18(e) ; and the road test, § 1512.18(p) (or the sidewalk bicycle proof test, § 1512.18(q) ) .(d)Attachment hardware. All screws, bolts, or nuts used to attach or secure components shall not fracture, loosen, or otherwise fail their intended function during the tests required in this part. All threaded hardware shall be of sufficient quality to allow adjustments and maintenance. Recommended quality thread form is specified in Handbook H28, "Screw Thread Standards for Federal Service," issued by the National Bureau of Standards, Department of Commerce; recommended mechanical properties are specified in ISO Recommendation R898, "Mechanical Properties of Fasteners," and in ISO Recommendations 68, 262, and 263, "General Purpose Screw Threads."(g)Excluded area. There shall be no protrusions located within the area bounded by (1) a line 89 mm (31/2 in) to the rear of and parallel to the handlebar stem;(2) a line tangent to the front tip of the seat and intersecting the seat mast at the top rear stay;(3) the top surface of the top tube; and(4) a line connecting the front of the seat (when adjusted to its highest position) to the junction where the handlebar is attached to the handlebar stem. The top tube on a female bicycle model shall be the seat mast and the down tube or tubes that are nearest the rider in the normal riding position. Control cables no greater than 6.4 mm (1/4 in) in diameter and cable clamps made from material not thicker than 4.8 mm (3/16 in) may be attached to the top tube.(i)Control cable ends. Ends of all accessible control cables shall be provided with protective caps or otherwise treated to prevent unraveling. Protective caps shall be tested in accordance with the protective cap and end-mounted devices test, § 1512.18(c) , and shall withstand a pull of 8.9 N (2.0 lbf).(j)Control cable abrasion. Control cables shall not abrade over fixed parts and shall enter and exit cable sheaths in a direction in line with the sheath entrance and exit so as to prevent abrading.43 FR 60034, Dec. 22, 1978, as amended at 76 FR 27888, May 13, 2011