The majority of parts are sold over the counter. They may require minor and skilled fitting. This is especially true on older guns where parts were hand fitted during assembly as labour was cheap. Later, tolerances were improved with modern manufacturing equipment and processes.
These parts are considered to pose liability or fitting concerns such as triggers, sears, safeties and breech bolts for example. There are parts that come very rough and require qualified fitting.
Manufacturers deal with these parts in different ways and the bottom line is the liability transfers to the gunsmith installing the part. This usually means the gunsmith must be fully licensed and have adequate liability insurance coverage.
Factory Only Restriction
Part is factory only. These parts are not sold. They are for factory replacement only and the gun must be returned to the factory for repair or to an established ARC (Authorized Repair Center).