This is the factory GLOCK .40 barrel that comes stock in the GLOCK model 23. It can also be used to convert the 23C to shoot as a non-compensated. Converting the 32 or 32C to shoot .40 s&w is also possible. Using it to convert the 19 to shoot .40 s&w is not safe as it will not fit into the slide properly. Calibers can only be converted down, not up. This barrel will work extended in the 27 and 33.