This shoe has a 1⁄4 inch - 20 thread hole to attach directly to a tripod, or the brass inserts (spigots) provided on many umbrella adapters. It can also be mounted on many off camera brackets.
This is the same shoe that comes as part of FlashZebra.Com umbrella adapter, item #0041.
The included thumbscrew can be used to retain flash units. The screw can often just be removed, as many flash units have there own retention devices that accomplish this task.
The grooves that the flash foot slides into sit above the bottom of the shoe (see image). On many (but not all) flash units this pulls the contacts on the flash foot above the bottom of the shoe. Most (but not all) contacts just dangle in air.
Price $5.50 + shipping