A tongue buckle used with grommets and a pass-through closure are the most common forms of fasteners currently found on full body harnesses.
Tongue buckle fasteners incorporate a traditional belt-buckle style closure. They have a prong that fits into a metal grommet which has been inserted into the fabric of the harness. This is a reliable method of closure with the condition of being binary in terms of sizing. There is no room for adjustment between the grommets. With this type of fastener, harness sizing adjustment is typically easier, especially when wearing gloves.
Pass-through, or parachute buckles, feature a male/female closure system. The male end passes through the opening in the female buckle creating closure between the two ends. Placement of the web through the buckle typically provides for a higher degree of custom adjustment than tongue buckle fasteners with grommets. Also, use of these buckles tends to reduce the overall weight of the harness depending upon the materials. Pass-through buckles are standard chest strap fasteners on the majority of harnesses.
The term “parachute buckle” is sometimes used to describe more contemporary fasteners utilizing a male and female attachment where the female component incorporates a mechanical latching system to hold the male component in place.