Hi Dean;

What I was promoting for the ROS's and routers was a speed control sold by Harbor Freight for 19.95 during their almost weekly sales . . . ;-) I've used mine for over a year and it's still working great. It's also nice for dimming my dual 500W quartz shop lites, I no longer have a perpetual sunburn on my neck from the full fury of those shop-warmers . . .

And yes, they only work with universal AC/DC motors such as those on sanders & routers.

Best Regards, Spidey