The ferro rod is 1.5" x 5/32" dia. (Exposed portion) It looks like it extends 3/16" into the handle.

The handle is 1.5" x 3/4" x 5/16".

I've carved off a bit of the rod already. I use the lockback indent on my Spyderco Salt I to spark it but I think the supplier sparker works better. But a jig saw or shortened hack saw blade works REALLY well.

This picture will give you some perspective - compared to the Scout version and to a magnesium block. Excuse the bad focus, my macro was having problems that day.
http://farm2.static.flickr.com/1021/929582581_b4ea197ca3_b.jpg

I googled the bsa hot spark - it looks to be about the same size, maybe slightly shorter ferro rod.

Hoods Woods has a smaller 1/8" x 2" rod sold in singles and 5 paks.
http://survival.instantestore.net/pd_mini.cfm