[FC] Turn signal cable not moving

[Chris & Bill Strickland]

yes, those are clutch head or butterfly screws -- drivers, often just as 
quarter inch hex bits, are still available in the smaller sizes such as 
you have experienced -- try googling to find some for sale or eBay. 
google Virtual Vairs for a seemingly relatively recent discussion and 
more info on this style fastener --
"clutch head" site:http://www.vv.corvair.org/pipermail/virtualvairs/

The problem with leaving the horn stuff in place is that the holes for a 
traditional steering wheel puller are underneath the horn parts.  1960 
cars use the same cable style arrangement, as probably do several other 
older GM products.

Godspeed!

Bill Strickland.