While these washers are perfectly good, let me tell you why I switched to shorter screws and smaller washers. The screw-set these washers pair with have a few quirks:
1) These washers will protrude 1mm outside your units when screwed down. That means after a few units the mm stack up and you'll be left with a 3-5mm diff in the total length of your sum of rack units, simply because the washers are too wide. Whilst a bit of force might solve your problem, I had difficulties mounting the last unit in an 8U rack because of this.
2) The Adam Hall screws these washers are to pair with bottom out in the Thon series racks if you're not using washers, which means you can't really skip the washers even if you wanted too — not saying you should.
Granted, not the biggest issue in the world, but I have 3 racks at home and switched to SKB series mounting screws/washers because of this. Hope this helped some of you.