Hey Guys! Sorry for the delay, I was trying to accumulate more information regarding your question.
We had a mutual customer reach out to Colt to inquire if the M5 pins were the same as the 901 pins. Since we already manufacture and sell the 901 pins, they could then be used for the M5. According to Colt, they are not the same pins. With that being said, I am seeing feedback from users on ar15.com and other forums that they have used our pins with success.
https://geissele.com/trigger-hammer-pins-for-colt-901.html
Unfortunately we cannot recommend them for the M5 and do not have plans to make dedicated M5 pins at this time. We have to defer to Colt's findings, and if they are not interchangeable per the manufacturer, we respect their expertise. Users could be finding success, but we are unsure of the reliability/long term use of unapproved modifications. We always recommend using the appropriately sized Geissele pins for our triggers.
We always want to make sure you have a reliable and functional product and hope you can understand our position.