Q:

During WW2, how dependent on Swedish Ball Bearings was Britain?

A slightly related question spawned this one. Sweden made a lot of ball bearings during WW2, which it exported to Britain and Germany. How many tons of ball bearings were imported from Sweden to Britain per year? How many tons was Britain manufacturing itself, and how many tons was imported from America?
I found this pdf and looked through it, but does not provide a full answer. It only speaks in relative terms and financial terms. It even seems to contradicts itself, saying 31% of British ball bearings were from Sweden in the first page, but later down says "Direct wartime imports from Sweden provided about 15% of all British ball bearings."
What we really need to know is how many tons of ball bearings were made in America and Britain. America was already convoying much stuff to Britain, and I suspect that if Sweden was totally cut off, American production could step up.

A:

They were obviously important enough to call for the implementation of Operation Bridford. According to that source "This operation resulted from the fact that the UK was to a degree dependent on Swedish ball bearings and also needed other specialist equipment to keep production plants running" so it sounds like it was not just about the quantity. The cargo is said to have been "ball bearings, speciality steels, machine tools and other items".
As for the volume the same source says "By 31 October Gay Viking had returned with 40 tons of cargo, the normal load. During the next five months, eight further successful round trips were completed, bringing the total cargo carried over the period to 347.5 tons against the planned for 400 tons. Over the same period of time, flights by aircraft carried 88 tons to the UK."
According to https://www.warsailors.com/freefleet/kvarstad.html "In March the department for aircraft productions announced that even as little as 100 tons of ball bearings would be sufficient to cover 75 percent of what was needed for 1200 Lancaster aircraft and 60 percent of what was needed for 1600 Mosquito aircraft. Some ball bearings were already being transported by aircraft from Stockholm, but it was far from enough to meet Britain's requirements." and "Operation Bridford had contributed greatly to meeting Britain's need for ball bearings and machinery, and also provided an essential portion of the equipment needed for the new factory being built in England, enabling the country to produce her own ball bearings."

