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eemort posted on r/standingdesk5w
So I started with this.... https://www.amazon.com but found the slides to be pretty garbage (literally broke themselves apart within a few months of babied use. But I really like the board it came with (though I wish it was wider and deeper). So I bought new slides from Home Depot that were rated for more weight... and so far so good but it's only been a couple of weeks and they're not noticeably stiffer or heavier than the old ones... so .... not a perfect solution really.... https://www.homedepot.com/p/Accuride-14-in. Luckily the holes for the brackets matched up exactly so I didn't have to drill new holes into the underside of my desk. Ebay also has a lot of kits so best of luck ~