MOTM

Square head screws are very popular in my part of the world. One 
thing I didn't see mentioned on McFeelys website is that you can 
often jamb a screw onto the screwdriver so that it doesn't fall off. 
This is incredibly useful when you are trying to insert a screw into 
a hole at various angles; gravity becomes irrelevant. Try doing that 
with a philips or a slotted screw head.

>They have square recesses in the heads, rather than a single slot or a pair
>of crossed slots. The manufacturer, McFeely's, can explain them far better
>than I can:
>http://www.mcfeelys.com/tech/faq.asp
>
>I use part # 0806-PSK-C for mounting modules.
>