Model M keyboards are held together with 4 small bolts that are deeply recessed within the back plate of the keyboard. You must use a long enough and thin-wall socket (or a nutdriver) sized at 7/32" in order to reach the bolts. Metric users could alternately use a 5.5mm equivalent tool (7/32" = 5.5563mm)
You can buy from sears, item number is 00943572000. Craftsman 7/32 in. Socket, 6 pt. Deep
Important to note, it must be "Deep"
I want to clean my model M keyboard. I have a mechanic's socket set, but I can't get the socket to fit in the hole to remove the screws. I also have a screwdriver that has replaceable tips, but it also does not fit. What is the correct size?