Helix angle the helix angle. The efficiency can be plotted versus the helix angle for a constant friction, as shown in the adjacent diagram. The maximum efficiency is a helix angle between 40 and 45 degrees, however a reasonable efficiency is achieved above 15°. Due to difficulties in forming the thread, helix angle greater than 30° are rarely used. Moreover, above 30° the friction angle becomes smaller than the helix angle and the nut is no longer self-locking and the mechanical advantage disappears. In helical and worm gears, the helix angle denotes the standard pitch circle unless otherwise specified. Application of the
Type 97 90 mm Infantry Mortar Light Trench Mortar, Manufactured in 1942, Osaka Army Arsenal". The Type 97 is approximately lighter than the Type 94 90-mm mortar. This weight saving was created largely by the elimination of the Type 94's recoil mechanism, which weighed . The bipod assembly of the Type 97 is lighter than that on the Type 94. There is a cover for the level on the yoke of the Type 97 which is not on the Type 94, and the sliding bracket of the Type 97 is hinged to permit its easy removal from the leg of the bipod, whereas it is integral