I have yet to see a BMX threadless setup in that diameter.

I used to race BMX and work on BMX bikes extensively, they were either
1" Threaded or Threadless (road standard)
1" Threaded (BMX/OPC Standard)
1 1/8" Threadless.

They seemed to have skipped the Threaded 1 1/8 that certain MTB's were using circa 1994.