The Flex Pro Professional Backing Plate with Drill and Dual-Action Adapters is a unique and versatile backing plate with interchangeable adapters; one makes the plate a drill chuck backing plate and the other makes it a pneumatic backing plate. Flexible Backing Plates minimize heat transfer, while it flexes just enough to contour to your vehicle's bends and curves. The Flex Pro 3 inch backing plate comes with both drill attachments (1/ inch shank fits most drills) that enables you to use it with any drill of your choice and Porter Cable or DA adapter (standard 5/16 inch). The Flex Pro backing plate is smaller than the pads to allow a generous lip of foam to protect the paint surface. Even if you turn the pad onto its side accidentally, there is an inch of soft, beveled urethane between the edge of the plate and the inner construction. Flex Pro Backing Plate provides the safest, most durable surface for your pads so that you get the best performance possible from your pads. These backing plates are built tough and even carry a one year warranty.
I got to use this backing plate twice before the insert stripped out spitting metal particles over the surface as I was going over. I didn't realize initially I thought maybe it was bits of the of but sure enough I did a great job marring the surface and took a ton of work to fix. Not only did I spend way more time on the job I also have to buy a new backing plate and pad because of this.
While the picture does not show threads, the black nipple shown on the backer plate is a protective cover over the threads! It pops right off. This is a nice touch such that the threads are not damaged during shipping or handling. Another nice touch is that it comes with two washers - don't throw these out! Use theses washers as spacers when one attaches the pad to the polisher - it gives extra space for the tightening wrench to get in between the pad and the polisher.
This backer pad also has a couple of other features that make it a nice backer:
1) The rigid plate on the polisher side is smaller around than the pad that came with the polisher. This allows the plate to be a bit more flexible at the edges for working curved areas.
2) The body of the pad is a more flexible material than the OEM backer plate. Again - better for working curves.
I am not sure why OP had an issue - perhaps they got a defective piece or another model that requires an adapter. I found an adapter on ebay priced at $3 plus $3 shipping and picked it up so I could buy any backer pad in the future.
So bottom line: Good backer plate, comes ready to use, has some nice features, good deal! Would buy again.
I bought this to use with 3" CarPro glass polishing pads on my Harbor Freight dual action polisher (Porter Cable 7424 knockoff), and it's perfect for that application. The combination of a small polishing pad on a small backing plate allowed me to get very close to corners and edges when polishing water spots off my windows. I used a larger pad and backing plate combination to polish the vast majority of the glass, but without the small pad and backing plate I would have had to polish the corners of my windows by hand, which would be a huge amount of work. A small polishing pad and backing plate can also be helpful in polishing out light scratches in glass, as the smaller size allows you to apply more pressure to the area.
I also tried the included adapter chucked in a drill just to try it out. It works just fine. For most applications I'll probably use my dual action polisher, but if you needed to polish something using a drill rather than a DA, this would allow you to do it. I suppose it could be handy for someone who just wants to polish headlight lenses or trim pieces and doesn't need a dual action movement to get the job done.