I have two related questions regarding my Thinkpad x220i and my SSD:
Should I be able to insert a M4 7mm into my Lenovo Thinkpad x220i?
If it is possible, what is the proper procedure?
Yes you should - the x220 does take in 7mm drives (as opposed to 9mm drives), though according to the service manual, SSDs require spacers, while hard drives use rubber rails. Considering the physical dimensions are the same, I'd guess you could just use whatever your drive has now. You just need to remove a screw and slide it out, then replace the current drive with a new one.
From the Lenovo service manual, Remove Battery First.
But what the manual does not show is removal from the caddy. But Lenovo says SSD's may use different rails, so you may have to find some on ebay or look in Lenovo Spare Parts