I have drilled a hole through the end of a Spark-lite before to put on a key chain but I don't know how long the solid portion of the Spark-lite "handle" is. Can you check for me?
I'm looking for the dimension from where the spring butts up against solid plastic to the end.
Sure!
On the Spark-lite, the spring actually doesn't go very far in. Only about an inch (or 3cm), leaving the last 3/4" (or 2cm) solid. It has a plug in the base, but it's held in very securely. I cut the spark-lite into two pieces towards the bottom, and tried to knock the plug out of both sections with a punch, but it held secure. Putting a keychain hole into it should not be a problem.
On the Fire-Lite, the spring goes nearly all the way to the bottom and the bottom plug is significantly smaller; therefore I would not try to drill a keychain hole in it.