The Fuse Blast ships with two blast orifice sizes: a 3 mm orifice and a 4 mm orifice. Early Fuse Blast units shipped with the 4 mm blast orifice preinstalled. All subsequent units shipped with the 3 mm blast orifice preinstalled. Formlabs recommends using the 3 mm blast orifice if you have an air compressor that does not supply enough pressure to adequately clean parts with the standard 4 mm orifice.

The 3 mm orifice and the 4 mm look similar from the exterior. Measure the inner diameter of the spare blast orifice that came with your Fuse Blast to determine which is currently installed.