This is an air compressor.
Design based on radial engines, this is a three-cylinder compressor using brass bushings for all joints. The piston integrates a one-way inlet valve, with the other one-way high pressure outlet screwed into the end of each cylinder.
Uses 6mm hardware.
1/4" ball bearings - mine are borosilicate glass, because that's how fancy I am 6mm flanged bushings - 6mm bore, 10mm diameter, 14mm flange, 6mm length, 2mm tall flange M6x15mm screws M6 locknuts M6 short nuts M6x20mm threaded rod