as it turns out I'm the one who has no idea what I'm talking about.
Joe

Now your talking Joe, you are now a fully paid up member here welcome to the club

Hood

Joe,

Well, I see my use of the secret code word 'slot' successfully confused everyone . .LOL!!

I don't know what to call it, Joe and in my case it is actually a round hole in the disk,  . . . . BUT . . . , the Mach manual calls it a 'slot' so I assumed that was the convention.

 . . "When in Machville . . . ."

Interesting discussion, thanks all.