I am looking for a serial number on a Armstrong performance mast 865 that I just purchased. I suspect a possible manufacture defect but was asked to send serial number. Cannot find the serial number anywhere on it. does anyone know where to find it ? thank you in advance for any possible answer or tip

It is on the mast plate. On the carbon side.
Top surface near the bolt holes at the back of the mast. it is hard to see as it is laser etched into the carbon. Get a torch or a light.