5.5mm is not a standard size for a metric allen key though, as standard they come in 1mm increments after 4.0mm
https://lmgtfy.com/?q=5.5mm+allen+keyhttps://handtoolessentials.com/blog/tools/hex-key-conversions-allen-wrench/https://www.homedepot.com/p/TITAN-1-4-in-Drive-5-5-mm-Hex-Bit-Socket-TIT15601/302071183https://www.truevalue.com/5-5mm-hex-l-keyEdit. Trying to keep post count down..
Ok. Nuts and bolts.. Did you sell tools? Or wrench on stuff for decades?
What do you consider "standard"?
If I can usually get it in a kit/set I call that a standard size..
Or easily find a single key/socket/T-tool
You're also just thinking America? Metric will be way easier to find in the rest of the world..
https://www.harborfreight.com/metric-t-handle-hex-key-set-10-pc-69370.htmlSize(s)
2mm, 2.5mm, 3mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 8mm, 10mm
https://www.harborfreight.com/13-piece-metric-ball-end-hex-key-set-96416.html1.27mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 8mm, 10mm
https://www.harborfreight.com/10-piece-hex-key-set-94597.html $2
1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 5.5mm, 6mm, 8mm, 10mm
https://www.homedepot.com/p/Husky-Metric-Short-Arm-Hex-Key-Set-10-Piece-HSAHKM10PCN/204153257 $5.50 set
1.5, 2, 2.5, 3, 4, 4.5, 5, 5.5, 6, 7mm
https://www.lowes.com/pd/Kobalt-13-key-Metric-Hex-Key-Set/503854841.5, 2, 2.5, 3, 4, 4.5, 5, 5.5, 6, 7, 8, 9 and 10 mm
https://www.matcotools.com/catalog/product/STW55M/5-5MM-7-32-HEX-SPINNING-T-HANDLE/Listed as 5.5mm and 7/32"
https://www.craftsman.com/products/hand-tools/hex-keys Oh. Craftsman no likely 5.5mm
https://www.matcotools.com/catalog/hand-tools/hex-keys/folding-hex-keys/Ok. I'll concede that it's not standard for big American brands
https://www.snaponindustrialbrands.com/DSN/wwwsnaponindustrialbrandscom/Content/PDF/Snap-on%20Industrial%20Brands%20CAT4%20236.pdfOnly have 2.5mm. Williams make their hex keys? And Armstrong makes their ratchets and sockets?