It does not have a lock. Like a lot of cheap Black and Deckers. Should be able to stick a small round object through a hole in the blade or lock it with vise grips as you did. The "arbor washer" may have been painted or another type of finish applied at the factory that has been worn off or even the arbor washer may have some wear that has allowed the blade to loosen just enough to allow the blade to turn in the shaft. Glad to hear that you found a cure.

OH les, wouldn't that be wonderful? I actually tried to think out how I could make it myself--if there's some sort of routing guide I could use to make it...I mean really I'd just need to do a rectangle and two little holes for the screws...hmmm... Otherwise, I think I'd have to have it custom made from tile I sent someone, and at that point it gets to be more than I want to pay. Nothing over around $30 at most. The RH ones are $9.50, so beside the trouble of driving down there, it would be done and moderately o.k. I'd like to see the Omnia ones, though, before I decide--to find out if maybe they're not beveled. I did find some extremely cool switchplates for the master bedroom, made out of cross-sections of walnut, with the bark still on them--can't wait for them to arrive (from eBay). They were custom made for someone, but then somehow they found their way into an eBay seller's hands--he doesn't know who made them. Now I'm going to think out more about making it myself...I have the tile saw, a sander to polish the edges...just need to figure out about the rectangle hole. The circular ones I'd be fine with.

I'd contact the company, Touch of Eco, but if you're talking about the bulbs they don't appear to be replaceable -- but it's hard to tell from the photo.

There are two very likely answers above. One is that the 8/32 was the right size, but the wrong number of threads per inch The other is that the screw is metric vs imperial. The closest size to a #8 would b a 4, the threads are measured by the number of millimeters between the threads. A good hardware store should have both an imperial and metric screw checkers. I have both in my tool chest. Saves me a lot of time and headache when looking for fasteners. https://www.amazon.com/Metric-Screw-Checker-2mm-7mm/dp/B0006NFUK6/ref=pd_lpo_2?pd_rd_i=B0006NFUK6&psc=1 https://www.amazon.com/Screw-Chekr-Thread-Gauge-Checker/dp/B0006NFUJW?th=1