0' x 4' Humbolt-Wedag #20U, Palla Vibratory Ball Mill. Category: Grinding Mills - Ball, Pebble, Sag, Mi... Seller: Machinery & Equipment Co. Location: Brisbane, CA. Mfr: Palla. Palla Vibratory Ball Mill, 8" diameter X 50" long (200 mm X 1249 mm). Manufactured by Humbolt - Wedag, model 20U, serial number 20181; was demo unit for trade shows.