IBM RT PC Options Installation page 118

3-10 Options Installation
5. For the numbered adapter slots, remove the screw holding the
adapter slot cover in place. Save the screw to install the adapter
later. Save the adapter slot cover in case you remove an adapter
in the future. You must have either an adapter or a slot cover in
each slot.
6. Unpack the adapter using the instructions under "Handling
Static-Sensitive Adapters" on page 3-4.