That covers were common in 00s bicycles and now in cheap bicycles with frames that allow disc and cantilevers or V´s. They use to cover the V´s mounts if you choose the disbrake bicycle option, like the caps in the forks compatible with disc and cantilever or V´s.
This reba has the caps:
Or my failed project, my ex Kula has caps too when it was brand new:
New frames always have canti stud covers (when needed) by I've never seen these ones with the spring pin plate covered too - not in 10,000 bikes!
Might be brand specific?
the folks that powder coat my frames have a supply of these for covering during painting so they obviously can be obtained en masse - however they look a bit naff for leaving on when using disc brakes - I would suggest removing the bosses entirely and inserting some decorative bolts in their place - https://www.ebay.co.uk/itm/354755581231
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