Fitment engine

The order it asks in

The engine asks four questions, in this order, and the first that settles the answer ends it.

1. A person's verdict. Where someone has checked a part on a gun, fits or not, the engine takes that answer and asks nothing else.
2. The caliber gate. A part rated for cartridges must be rated for one this gun fires, and the gun's barrel must meet the rating's minimum length.
3. The mounting. Every group of standards the part needs must be met by an interface the gun has, at a position the part may sit.
4. One adapter. A group nothing on the gun meets is tried again through an adapter the gun can mount directly: one hop, never two.

The caliber gate

A suppressor, a muzzle device or a magazine carries the maker's ratings: the cartridges it is built for, and for some a minimum barrel length. The gun must fire a rated cartridge, and its barrel must be at least the minimum. The gate is never bridged by an adapter and never inferred: a part rated for 5.56 is refused on a 9 mm pistol however well its thread matches.

A part with no ratings is held to its bore instead: a bullet wider than the part's stated bore is refused. A rated part is not held to its bore, because makers state the bore as a calibre class rather than the measured hole, and holding a rated part to it refused parts the maker rates for the cartridge.

Mounting, placement and adapters

A part lists the standards it needs in groups. Any one standard in a group will do, and every group must be met. The WILD1 light needs one group: a Picatinny rail or a Glock universal rail, under the barrel.

Where a part may sit is a matter of the part. A magnified optic keeps to the top of the receiver, where its eye relief can be met; an unmagnified one may also sit forward on a handguard rail. Some kinds of part treat two positions as one surface, with the declared one preferred:

When nothing on the gun meets a group, the engine tries every adapter the gun can mount directly. The adapter must pass the caliber gate itself, and what it provides must sit where the part may go. Threads and magazine wells are never bridged. Every route that works is returned: direct before adapted, the part's preferred position first, then by confidence.

Confidence and evidence

A fit's confidence is the lowest confidence among the interfaces it uses, so one weak interface caps the whole answer, and a caller can hide weak fits by asking for a minimum confidence. A fit's evidence is the weakest source among them, on this ranking:

Worked example: two parts on a Glock 17 Gen5

The Glock 17 Gen5, whose interfaces all come from its Gen5 9x19 platform, against two parts as their records state them. Both answers are the engine's own, run as the page loads.

The light mounts on the rail under the barrel, and its confidence is the rail's own, 0.9, with the platform as its evidence (inherited:platform). The suppressor never reaches the mounting questions: it is rated for 5.56 and .223 only, so the caliber gate refuses it before its thread is looked at.