DIN blank caps function just like Tri Clamp End Caps, but for the DIN standard. They fit into the welding male with a gasket, and have the same bevel as welding liner but are solid. Unlike the welding male or liner, blank caps are not welded and thus do not need an imperial inch-based size. They simply fit into their respective (25mm, 40mm, etc...) metric counterpart. The round nut then presses the blank cap and welding male together compressing the gasket and forming a tight seal.
Incorrect sizing is common with DIN 11851 fittings. Please review our DIN 11851 Guide for assistance in sizing your DIN 11851 fitting.