These mag bases are designed to adapt your stock P365 12 Round magazines to fit in the X Macro grip module (they will work in any smaller grip module as well). Please check the dimensions of the mag you have against the image here so verify you have a standard 12 Round Magazine.
They are machined from aluminum and hollowed out to be lightweight if that's what you want OR you can add Tungsten weights into the cavities to make back the weight lost from the missing rounds. Adding weights reduces felt recoil and makes the mags drop faster and more reliably from the gun. (Weight kits sold separately).
Add functionality to earlier magazines and maintain "compliance" when used in grip modules that were designed for higher capacity magazines. Base blates are bolted through and into an internal locking plate to allow tactical reloads and normal range use (dropping on concrete/rocks may damage the mag well cosmetically and is not covered under warranty).
Made in the USA to be very robust these will put up with abuse and come with a Lifetime factory warranty against defects in design or manufacturing (does not cover cosmetic issues from use or dropping mags).