M35 ET air-vent bushing. As with all vents on M35s, the air-vent bushing is pressed into to an opening in the shell. The air-vent bushing is a separate part.

M35 Quist air-vent bushing. Note the shape and size compared to the ET air-vent bushing above.

M35 SE air-vent bushing. Slightly different compared to the ET.

M35 NS air-vent bushing. This bushing has flatter profile and it can differ in size on NS helmets.

M35 NS air-vent bushing right side (the same helmet as the picture above). Note the smaller vent hole compare to the left side vent hole in the picture above.

M35 EF air-vent bushing. This bushing is often poorly manufactured compared to bushings of other manufacturers.

M40 ET ridged air-vent.

M40 Quist ridged air-vent. Note the larger diameter and the smaller hole on the air-vent.

M42 hkp (SE) ridged air-vent. Note the higher profile of the air-vent.

M42 NS ridged air-vent. A less dominant stamped air-vent compare to the others. Low profile and smaller diameter.

M42 EF ridged air-vent. This one has a even lower profile than the NS air-vent above.

Size ink marking on liner in an M40. The liner is manufactured by F.W. Müller Jr., Berlin.

Size ink marking on liner in an M35. The liner is manufactured by Schubert-Werk K.G, Braunschweig.

Size ink marking on liner in a late M40. The liner is manufactured by Schubert-Werk K.G, Braunschweig.

A non-circled ink size marking in an M35. The liner is manufactured by Metal Lederverarbeitung W.Z. (Werner Zahn, Berlin).

A non-circled size ink marking in an M35. The font differs from the picture above. This liner is manufactured by B & C (Biedermann & Czarnikow, Berlin/Litzmannstadt).

A non-circled size ink marking in an M40. This liner is manufactured by B & C (Biedermann & Czarnikow, Berlin/Litzmannstadt).