Passage: Thüringen was present during the fleet operation that resulted in the battle of Jutland which took place on 31 May and 1 June 1916. The German fleet again sought to draw out and isolate a portion of the Grand Fleet and destroy it before the main British fleet could retaliate. During the operation, Thüringen was the second ship in I Division of I Squadron and the tenth ship in the line, directly astern of the squadron flagship Ostfriesland and ahead of another sister Helgoland. I Squadron was the center of the German line, behind the eight König- and  Kaiser-class battleships of III Squadron. The six elderly pre-dreadnoughts of III and IV Divisions, II Battle Squadron, formed the rear of the formation.Shortly before 16:00, the battlecruisers of I Scouting Group encountered the British 1st Battlecruiser Squadron under the command of David Beatty. The opposing ships began an artillery duel that saw the destruction of Indefatigable, shortly after 17:00, and Queen Mary, less than half an hour later. By this time, the German battlecruisers were steaming south to draw the British ships toward the main body of the High Seas Fleet. At 17:30, the crew of the leading German battleship, König, spotted both I Scouting Group and the 1st Battlecruiser Squadron approaching. The German battlecruisers were steaming to starboard, while the British ships steamed to port. At 17:45, Scheer ordered a two-point turn to port to bring his ships closer to the British battlecruisers, and a minute later, the order to open fire was given.While the leading battleships engaged the British battlecruiser squadron, Thüringen and ten other battleships, too far out of range to attack the British battlecruisers, fired on the British 2nd Light Cruiser Squadron. Thüringen and Kronprinz engaged the cruiser Dublin, though both ships failed to score a hit. Thüringen fired for eight minutes at ranges of 18,600 to 20,800 yd (17,000 to 19,000 m), expending twenty-nine 30.5 cm shells. The British destroyers Nestor and Nomad, which had been disabled...

Question: What size rounds did Thuringen use?
30.5 cm