DIN gaskets are designed specifically for DIN fittings. The underside of the gasket is flat and butts up against the welding liner's flat face, while the top side has a rounded edge which fits nicely into the groove of the welding male. The round nut then joins the liner and male compressing the gasket creating a tight seal. Gaskets are matched to other DIN fittings based on the metric sizing (Ie: A 40mm gasket is used for any DIN fitting that is 40mm, including any Imperial (inch-based) fittings that are also listed as 40mm).
While we are prohibited from recommending a gasket type, we do offer a Chemical Resistance Chart (new window) that matches the resistance level of gasket materials to the different chemicals / food products you may be using. We may suggest using an A- or B-rated gasket for your particular application.