Question about making trolling flies

[Patriot]

I've been making my own flies for over 10 years, pretty simple to build them, takes less than 2 minutes.

Anyhow, some time ago I purchased a few Howie flies and noticed a plastic sleeve over the fly material.

Does anyone know if there's a tool that you use to put that plastic sleeve on with? I've always used thread but figured I'd ask.

 

Thanks

[Legacy]

I use shrink tubing to cover mine.