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 90 Kyū-maru to the left of the main gun. The profile of the Type 90 is similar to the German Leopard 2A4 and it uses modular ceramic and steel composite armor, common in contemporary tank designs. The adoption of modular composite armor design facilitates the upgrading and exchange of the armor, and its frontal turret armor is rated at 380mm of effective thickness against kinetic energy penetrators, while the upper frontal hull armor is rated at 320mm of effective thickness against kinetic penetrators. The Type 90 is smaller than most main battle tanks with a height of , a width of ,