Time-test viscosity tubes are frequently referred to as ASTM D-1545 Tubes.

Time-test tubes are scored in three places, 27 mm, 100 mm and 108 mm. The score mark at 27 mm is used for a 73 mm timed bubble travel. Time-test viscosity tubes are also subjected to additional testing procedures to ascertain the 10.65 mm bore which is very critical for precision measuring.