These are high quality SGM Tactical magazines.
This quality replacement magazine for a Glock is constructed from steel and polymer just like the originals. Works with all Glock 40 calibers including those with ambidextrous magazine releases and can be rebuilt using factory magazine parts.
Note: Like many new magazines, these have an extremely stiff spring from the factory. It may not be possible to initially load them to capacity. Loading half of the listed capacity and leaving it loaded overnight before the first use will ease future loadings.