How did the Allies determine balls bearing were a "choke point target"?

[DogFather]

The other target was oil and that's more obvious. How did they figure out ball bearings could stop the whole war effort by Germany?
That never really worked very well, but the the lack of fuel had a large effect on the German war effort. That was true with Japan as well.
Anyone know how that was determined?

 

[FLYBOYJ]

"The Bavarian city of Schweinfurt, with its heavy concentration of ball bearing factories, was a classic example of one of these so-called panacea targets. It was obvious that anti-friction bearings played a vital role in any industrial economy, but 1940s-era German machinery was believed to be more dependent on ball bearings than most. It was estimated, for example, that the German aviation industry consumed an average of 2.4 million bearings per month. The fact that bearing construction was concentrated in just a few plants, with Schweinfurt accounting for more than 40 percent of production, made the ball bearing industry in general-and Schweinfurt in particularan obvious target. Making Schweinfurt even more attractive was its small size, which would make it easy for bombardiers to locate and hit the bearing plants-a factor that also made it a poor target for Harris' night bombers. German planners had belatedly realized the vulnerability of the bearing plants and began making plans to disperse them, but to do so would take time as well as disrupt production of the precious bearings."

World War II: Eighth Air Force Raid on Schweinfurt