I made one out of a thick Nylon washer from the hardware store so I wouldn't scratch anything. Sort of like a plastic nickle. It works fine.

None of the washers in the store fit so it just required a little sanding. I heard a real nickel works too.

I don't know what the slot thickness is, but there might be a hollow ground screwdriver bit out there for gunsmiths that would fit too, but the chance of it slipping discourages me from seeking one out or trying to fabricate one.

Tom:

I use gunsmithing screwdrivers for all of reel work however; unless I am thinking of the wrong screw, the screw in question has a slot width of approximately .077”, (more than likely 2 mm as the reels are English), and a diameter of approximately .340” or 8.5 mm.

I don’t know what Hardy uses, but the closet gunsmithing screwdriver bit I could find is a Brownells Maga-Tip bit #340-8 that has a blade thickness of .070” and a blade width of .340”.

I have that bit and while it fits, it’s a TAD looser than I would prefer and if it slips…

That’s why I made a “plastic nickel.”

Ron:

I assume that is the screw in question and the one I am referring to.

On at least one of my older 1980's version LHW Perfects, the direction to loosen the screw was stamped in a circle around the screw.

While I am the furthest thing from an expert, the first time I saw a Hardy with a screw was when I bought the 3-3/8" LHW Perfect I have. All of the RHW Perfects I lusted for but couldn't deal with, didn't have the screw.

Now it seems to be standard on LHW & RHW versions.

Beautiful ! Great detailing right to the reverse thread reminder on the screw. It is a little scary to think of anything made "just like an MG," though. I would feel better--the proof being evident in that reel--if it was said that they tried to build an MG with the quality of a decades-old fly reel. I have an acquaintance, in his mid 90s, who has owned an MG since purchasing it new. He says it starts and runs and has been stored with reasonable care. Since I met him 30 years ago, he has told me he would be driving it again soon, after he replaced the clutch. I saw his son the other day, who said his Dad hadn't gotten around to that yet. I think he gets too busy fishing using "vintage" tackle that outlasted the MG.

I am a dub with tools these days, gunsmithing screwdriver set or not. So I like Bamboozle's solution, having used a ruler in that way for my Ocean City. I fixed that one when it was handed down from my grandfather. I have a couple others similar that I might fix soon.

Re: the original question.

When I owned Bougle reels & once a Perfect, I was concerned about deforming Hardy's NS set-screw slots with my standard slot drivers. I've seen a number of stressed slots on friend's Perfects & Bougles.
Why not use coins?

On my travels to Cuba & some Central European countries, I collected left over change. Many of the low value coins from these countries are made of soft aluminium.
If I remember right, I used a Cuban V (5) Cetavos or a Hungarian 50 Filler piece, that not only fit the width of the NS set-screw's slot perfectly, but also followed the curvature machined into the bottom of the slot. This allowed my coin "screwdriver" to engage deeper into the slot for a better grip. The soft aluminium coin's edge would be damaged first, before the NS screw's slot.
You do not have to torque the set-screw very hard to securely lock the spool in place.

I had nothing significant to add, just my own experience.