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Question: Can I use this to mount a vesa 400x400 tv to a tv stand with fixed vesa 800x400 mount?
Document: Successfully converted my vesa 200 tv mount to use my new vesa 400 tv. I recommend this as long as your mount will support the weight.
Moved in a house that already had a wall mount installed on the wall but wasn't the right VESA size for my new Viore 32 LCD tv, which has a vesa of 200 x 400 ..after researching the old wall mount online and making sure it could hold the 33 LB Viore  " and being told by many sales people and online merchants/techs that you can't buy an adapter "  of course they just wanted to sell a new wall mount ! I researched more and  found this adapter on amazon .
It was a little bit confusing at first of how to put this together but next time I'll make sure to read the instructions. However, my tv is a 32 inch and the mount that I bought was the right size but it needed these 4 metal plates for my tv to fit. Good thing I bought them because it helped a lot. It's strong, clean and I can use it again when I get a bigger tv lol. But it's a great product.
After I had already ordered my "VideoSecu TV Wall Mount for most 15" to 27" LCD TV 18-Inch Extending Full Motion Wall Mount Bracket" I quickly discovered I needed extender brackets to mount my tv. The brackets matched up perfectly, however, the screws did not. You would think a product that is from the same company that is to be used in combination with that specific product line would come with universal screws. A quick trip to the Home Depot fixed that, but annoying just the same.
Using this with the Audio 2000 Ast422y and works perfectly. Holds my 47&#34; tv on a 100x100 vesa bracket. Would recommend.
I checked a few stores nobody has these. I thought about making some but for the price just buy it,When u put it together make sure the screw-drive head is facing out and the nut is facing the tv. You can't use the screw-driver, on the TV side. It has a slight bend in the metal so the nuts don't hit the tv.
Oops, I bought the wrong mount for my TV. I got a great deal on the mount, but I needed a larger VESA size. This adapter fixed the problem!
I bought a TV stand off of craigslist which included a vertical mount, but the mount was made for much bigger TVs. So I first checked a few brick and mortar stores for some kind of adapter. Of course they only carried mounts, not mount adapters. Not sure why I even bothered, it always ends in disappointment and a visit to Amazon.
I used with an older sanus vm400 (200vesa) wall mount and an LG 42 inch (400vesa). Sanus converter bracket  supported every other configuration EXCEPT 400-400 vesa; they wanted me to buy a new bracket. VideoSecu adapter takes a little patience to get adapter plates aligned with TV/mount because the bolts are a little smaller than holes which allows movement until tightened down. However the adapter does the job and the savings is well worth it.
took me a few minutes to figure out the proper orientation.... but got it.they work great... holding up a 32" vizio on a articulating wall mount that only had 100mm vesa mount.
Answer: Yes