I purchased a 'Blackburn Ex 1 Disc Rack' and 'Axiom Seat Collar w/ Rack Eyelets'.  The installations instructions for the rack could be a bit more detailed; however, with some experimentations, the rack fit quite well.  Note the rack came with lots of associate hardware.  I used only part of hardware and presume the rest would be for other bike fittings.  I used it for 2 months without any issues preparing for a short trial tour in May and then a longer tour in July.  Unfortunately, both were canceled due to the pandemic.  I took the rack off the bike and placed it in storage for next year.  I do know others (with this rack) who keep it on their bikes permanent to carry extra "stuff" on regular rides.  I am very pleased with the Blackburn rack.  There is a minor limitation worth noting.  The rack attaches at 2 points: at the seat collar and on the rear bike skewer that is provided with the rack.  Fixing a flat on the rear tire will require detaching the rack to pull the wheel for the tire repair.  This will require a little extra time to repair a flat.  My plan was to put a new tire on the rear before the tour to minimize the need to repair a flat.  Hope the preceding helps and May The Wind Be To your Back.