Hood Release Knob

From Citroen SM Wiki

If the original pulls off or breaks, there are several replacement options (other than finding an OEM one):

Use a Universal Radio Knob

Unhook the cable at the hood release to give you some slack, then unscrew the little brass bit from the end of the cable at the driver's seat. Clean off the remains of the rubber and go to radio shack and get a universal radio knob for $5. Attach the knob to the brass bit with the setcrew in the knob, then thread it back onto the end of the cable.

(Courtesy John Titus)

Cross

The knob is the same as a late DS choke knob.

Aftermarket

SM World sells a replacement knob machined from solid brass with a black powder coating..