Size
The same reason rifles come in different sizes. Smaller gauges generally have less recoil, throw a smaller pattern, and some people just prefer different sizes.
9mm. 2,4,6,8
guage refers to the size of the shell any particular shotgun will fire.
They were a brand of Crescent Firearms. They probably came in 12, 16, 20 and .410. It is possible but unlikely they came in 10 and 28 gauges. It is exceptionally unlikely but possible they came in 32 gauge. They seem to be running around $300 in 2012.
Auto Meter manufactures many different kinds of gauges. Mostly they specialize in different styles of tachometers, the meters that measure speed on the dashboard of a car. They manufacture other gauges such as oil and engine temperature gauges and gauges specifically made for boats.
Conventional shotguns run from 10 gauge (very big) to a .410 (smallest). The most common are 12 and 20 gauges, a little less common are the 16 gauge and .410 (.410 = 67 gauge). Some of the less common gauges are 32, 28, 24, and 10 gauge. There are also monster 'punt' guns usually 6 or 8 gauge mounted to a boat. The smaller the gauge number, the bigger the gun.
The distance between the two tracks. There are many different gauges around the world.
Guns come in many different varieties; among them are pistols, rifles, handguns, and shotguns.
A bore gauge is a tool used to measure the sizes of various holes. There are no different kinds of bore gauges, but bore gauges do come in a few different sizes.
Transshipment of fright.
There are a number different gauges for different products. For steel sheets, the gauge ranges from 3 to 38. For aluminum, the gauge ranges from 6 zeroes to 40.