10.1.3 The acceptability of a guard is judged with respect to its general serviceability and with respect to the shape and size or both of the openings in it, in conjunction with the distance of the guard from the heating element and the other high-temperature parts mentioned in 10.1.1. Except as noted in 10.1.5, an opening in a guard is considered to be acceptable if, with the heater in any intended operating position, the following conditions are met: b) The shape and size of an opening which permits the vertically downward entrance of a bar probe 1/2 inch (12.7 mm) wide and 1/16 inch (1.6 mm) thick, see Figure 10.2, are such that a triangle probe 1/16 inch thick and in the form of an isosceles triangle having a base of 2-3/4 inches and an altitude of 5-1/2 inches, see Figure 10.3, is prevented from touching the heating element and the other high-temperature parts when the triangle probe is inserted, apex first, in any manner. The testing of an opening with the triangle probe applies also where the vertically downward insertion of the bar is prevented by the construction of the guard, the use of an additional barrier, or both, unless the vertically applied bar tends to be deflected outward – that is, away from the guard.