Anyone know the thread size on a shiffter for a 78' SC?
 

Picking out a new shift knob for the SC and I have no idea what the thread size might be. Anyone have any idea?

from the factory, the 915 shift rod/assembly uses a shift knob that's held on by a crush sleeve (friction) and doesn't have/use threads -- you should be looking for a knob that's designed for a 915 and either uses some sort of Allen bolt to affix/secure or uses the crush sleeve arrangement. I went with a wood knob (made from stacked broken skateboard decks) that uses a crush sleeve to hold it onto the shift rod -- note that you'll likely destroy the original knob while trying to remove it -- search the forums for instructions/details

I know of only one car brand that uses a crush sleeve.
Most people do not want to destroy their shift knob to remove.

Shift knob manufacturers want to sell as many knobs as possible. Most use a more universal method of attaching a round object to a tube. Makes sense.

Sherwood