The Pentagon Magazine Coupler Kit provides a unique external coupling option for the 10 Rounds Ultimag AR magazines and is provided with five Ultimag 10R magazines. - Advantages: - Highly ergonomic design - Durable high grade polymer construction - Maintains 10 cartridges limitation - External coupler - does not replace magazine floor plate - Compatibility: - M16/M4/AR15 variants - Included in the kit: - 1x PMC Magazine Coupler - 5x Ultimag 10R Magazines