IBM X23 - Manual (Page 58)

FRU replacement notices
This section contains notices related to removing and
replacing parts. Read this section carefully before replacing
any FRU.
Screw notices
Loose screws can cause a reliability problem. The IBM
ThinkPad computer addresses this problem with special
nylon-coated screws that have the following characteristics:
v They maintain tight connections.
v They do not easily come loose, even with shock or
vibration.
v They are harder to tighten.
v They should be used only once.
Do the following when you service this machine:
v Keep the screw kit (P/N 05K4841) in your tool bag.
v Always use new screws.
v Use a torque screwdriver if you have one.
Tighten screws as follows:
v Plastic to plastic
Turn an additional 90 degrees after the screw head
touches the surface of the plastic part:
90 degrees more
(Cross section)
v Logic card to plastic
54 ThinkPad X20, X21, X22, X23, X24