Also known as a fiberglass pen.
Here's an example: http://www.radioshack.com/pro-grade-abrasive-fiberglass-pen/2760039.html

I recently got the type from the link, and it quickly made its way toward the top of my "must have" list of tools, just below my Optivisor and sprue cutters, and about even with my scalpel blades.
Wonderful tool, countless uses. The latest use I've found for it is for scuffing up those too-shiny vinyl tires.

Anyone else out there use these?

yeah I use 4mm and a 2mm pens I like the fact you can adjust how abrasive they are by how much of the fibres are exposed, I find they are very good at sanding around textures and details on kits without destroying them.

Hadn't thought about using them on vinyl tyres will have to give that a try.

Hi Floyd

Yep - I wouldn't be without one. They are probably both my favourite and most hated tool - favourite, because they are so useful in sanding and refining details - and hated, because they literally are a pain if the glass gets into your skin!

All the best

Rowan

I am likely telling you how to suck eggs, but you do know that these are supposed to be used under soapy water in order to prevent the issue Rowan mentions and to protect your eyes and prevent inhalation.

Neil - It's like an adjustable sandpaper, isn't it?
One of my biggest uses is for the marks left by liquid cement after it dries. Just let the bristles out a little, and the worst it does is dull the plastic. I think that's what gave me the idea to try it on vinyl tires. I haven't tried it on every type, but the ones I've used it on look good. Now to see if they disintegrate in a few years...

Rowan & Darren - haven't had any issues yet, but I think that mine's probably one of the nylon types and not true fiberglass. I'll keep the info in mind, though.

It's definitely one of those tools that you never knew you really needed - until you've used one.

They are great but as somebody said watch out for the fiber glass pieces . Must clean after each use .