A miter gear is a special case of a bevel gear where both mating gears have the same tooth count, giving a 1:1 ratio. Their only job is to redirect a rotating shaft — almost always through 90 degrees — without changing speed or torque. If bevel gears are the general family, miter gears are the "elbow joint" of the mechanical world.

Because the ratio is 1:1, both gears are the same size and both pitch cones have a 45-degree pitch angle (for a 90-degree shaft intersection). This symmetry has real consequences: the design equations simplify, tooth loads on both gears are identical, and either gear can be the driver.

Tooth geometries you'll encounter:

• Straight miter: Cheapest, easiest to make, but noisy above ~1000 RPM because teeth engage abruptly along their full length.
• Spiral miter: Curved teeth engage gradually, running quieter and carrying more load — at the cost of generating axial thrust that the bearings must absorb.
• Zerol miter: Curved teeth but with a zero-degree spiral angle. Smooth like spiral, but with straight-cut thrust characteristics. Common in aerospace.

Real-world example: A hand-crank drill press feed handle. You turn a horizontal wheel, and a pair of miter gears redirects that motion 90 degrees down to the vertical quill shaft. No mechanical advantage is needed — you already have plenty from the rack-and-pinion — just direction change. Similar setups appear in right-angle drive attachments for power tools, marine transmissions connecting a horizontal engine to a vertical propeller shaft (via a lower-unit gearcase), and Rotisserie mechanisms in ovens.

Selection rule of thumb — pitch cone distance: The mounting distance is set by the outer cone distance A₀, which for a 90-degree miter pair with pitch diameter D is:

A₀ = D / (2 × sin 45°) ≈ 0.707 × D

Example: a 2-inch pitch diameter miter gear has A₀ ≈ 1.414 inches from the shaft intersection point to the outer heel of the tooth. If you get this mounting distance wrong by more than a few thousandths, tooth contact shifts off the pitch line, backlash spikes, and the gears howl and wear rapidly.

Watch out for: Miter gears must be mounted so both shaft axes intersect at a single point — even small offsets destroy tooth contact patterns. Also, the small tooth count (typically 16–20 teeth) means undercut and reduced beam strength; don't push them past their published torque ratings.