Joseph says that he translated the BoM with the Urim and Thummim.
Joseph Smith in Elders' Journal of the Church of Jesus Christ of Latter Day Saints (July 1838): 43, The Joseph Smith Papers website, accessed August 11, 2021
I obtained them, and the Urim and Thummim with them; by the means of which, I translated the plates; and thus came the book of Mormon.