UAC is a Hong Kong brand that specifies in the production of competition modification parts for airsoft guns, and due to the popularity of the TM M4 MWS series, they have introduced the Enlarged bolt stop, Enlarged Ambi-Magazine Catch, Ambi-Selector and a Race Trigger. All of the items are constructed with aluminium so they would be light weight and durable.

The Bolt Stop - A type is an enlarged bolt release button with non-slip pattern allow fast access to release the bolt after reloading. This is one of the essential parts for fast reloading.