m303Why Choose the M303? Lower Emissions Simplified Installation Minimal Lifecycle Maintenance. Gallery. Description. The M&J Valve Model M-303 is an advanced desn slab gate valveBÖHLER M303 HHHARD is a corrosion-resistant Cr-Mo steel, pre-hardened to approx. 1200 MPa with optimised toughness and polishability for processing corrosive moulding