Manfrotto 118 Male Spigot Mounting Adapter, why the hole?

[gl600]

Hey,
I bought one of these:
Amazon.com: Bogen - Manfrotto Swivel Umbrella Adapter (Lite-tite) Replaces:2905: Camera & Photo
and it came with this:
Amazon.com: Manfrotto 118 Male Spigot for 2905 1/4-20-Inch Male and 3/8-Inch Male 26mm Long Adapter - Replaces 3107: Electronics
Why does it have a hole?
When I use it to mount a flash, sometimes the bolt that pushes against the piece to secure it will go through the hole.
?
Thanks