What size is the tiny ball bearing used in SRAM rim-brake caliper quick release detents? SRAM road rim-brake calipers (mine are specifically Rival from 2011) have a quick release lever to facilitate wheel changes, as many calipers do.  The SRAM QR lever has detents which make a little "click click click" noise and feeling as you rotate them.  Today I found out how that detent works, and wish I hadn't.

You see, I was replacing the M4x6 button-head screws on the QR "axle", as they were quite rusty (see SRAM Rival brake caliper screws/bolts are rusty, how to replace?).  I had unscrewed one of them a couple weeks ago to check the screw size, ordered the screws, and now had them in hand.  When I unscrewed the second one, I heard a little "ping" as something fell down on the floor.  I searched around for it, and behold, it was a tiny ball bearing!

So in the process of opening up the first brake a couple weeks ago, I'm sure the ball popped out of it, and the floor has been vacuumed since then so goodbye.

The question is: can someone tell me what size the ball bearing is?  I can tell you it's roughly 1-2mm, but I don't have sufficiently precise equipment to measure it.  Bonus points for a link to purchase replacements (in small quantities!).

As an aside, this design seems comically bad: they use a screw which for some reason is more prone to rust than any of the others in the groupset, and when you unscrew it there is this tiny metal ball sitting on a tiny metal spring waiting to eject it from the assembly.  It's no wonder why they don't call out these parts in the service manual!
The balls are 2mm in diameter.

How do I know?  Well, I found a bearing supply shop, and asked them to see some of their smallest balls.  I bought one 2mm ball and one 3/32" (2.38mm) ball for all of 20 cents.  The 3/32" ball was slightly too large to fit in the hole, so I tried the 2mm one, and bingo--a perfect fit.  Putting the QR mechanism back together is a pain because the tiny 2mm spring wants to eject the ball again, but with the brake facing straight down it's doable.