They are balls (ooer missus), but no fear of chasing them all over the garage floor. They are set in a plastic holding ring which drops on top of the race after you've mullahed it down the headstock tube. Top and bottom are exactly the same bearing/race.
They are easy to fit, after you've got the old race of the headstock tube. I put mine in the oven for 10 minutes and then get my thickest leather gloves, a couple of my Dad's best chisels which he's lost and hammer them under the race until they start to move. then the race just lifts off and you can hand it to any unsuspecting helper without gloves.
For the first time ever I decided to use a torque wrench to set the things. I bought a halfords socket that was the same outside diameter as the castellated adjusting ring and got a grown up to angle grind it to fit (angle grinders scare me). Seemed to work okay and also happens to fit my DR350.
3 Africa Twins/280,000 miles. If it's happened to one of mine, it's gonna happen to one of yours.....eventually.
1 Varadero/34,000 miles ridden (of 57,000 miles on the bike), it's all still new to me!