This is the X Macro 17 round magaine but it fits in all models of the P365, including our grip module. 

Find it here at Sig: P365 17RD MAGAZINE (9mm)

Additionally, if you are pair this magazine with the Sharps grip module for the P365X/XL, you may want to pick up this base plate adapter:

P365 X-Macro base plate adapter for P365X & P365XL - SHARPS BROS