Concealment
Glock pistols come in three basic sizes: standard, compact and subcompact. The dimensions of the standard Glock is approximately 7.5 inches long and 5.5 inches. Exact dimensions vary slightly between models. The advantage of the standard size is that it's easier to control and has a larger magazine capacity; the disadvantage is that it's hard to conceal. The compact-sized models are slightly smaller and approximately half an inch shorter in both length and height. The subcompact models were specifically designed for concealment and are approximately 6.75 inches long and 4.75 inches high. The advantage of the subcompact is that it still has a standard magazine capacity of 10 bullets, even among larger calibers.
Safe Action
Glock pistols all have a "safe action" system. This is a series of three redundant safeties that prevent the pistol from firing unless the trigger is pulled. While they are being carried, Glock pistols are uncocked, meaning that the firing pin is not engaged and the weapon is incapable of firing. As you pull the trigger, the pistol's internal safeties are disengaged, the firing pin engages and fires the bullet. As soon as you release the trigger, the safeties reengage and the firing pin disengages.
Caliber
Glock handguns are available in seven different calibers ranging from the small .380 to the large .45. Glock has standard-sized and subcompact models available in each caliber. The pistols all have staggered stack magazines, which allow them to hold a great capacity. The one exception to this rule is the Glock model 36, which is a subcompact .45-caliber pistol with a straight stack magazine with a six-round capacity. The advantage of this pistol is that it has a width of just 1.13 inches, which makes it slimmer and easier to conceal.
Carry Options
The Glock line with the most options is the subcompact. These pistols can be carried on a hip holster without being too intrusive, a shoulder holster or an ankle holster. The small size can even allow you to carry a Glock subcompact pistol in a jacket pocket. The standard and compact models are also concealable when worn with a hip or shoulder holster, but to a lesser degree than the subcompact.