The manufacturer code is stamped on the inner rim on the left side close to the chinstrap bale. ET is the abbreviation for Eisenhüttenwerke - Thale (later ckl and CKL) who manufactured M35, M40 and M42 models. The number "62" indicates the shell size.

The same producer, Eisenhüttenwerke - Thale, this time with a ckl stamp. The change in manufacturer code from ET to ckl occurred during final production of the M40 and initial production of the M42 models. M42s  can be found with ET stamps and M40s with ckl stamps. The change to an ordnance code (ckl) was to protect the identity and location of the manufacturer from the Allies. Notice the lot number «2938». The lot number indicates the particular batch of sheet steel that was used when a quantity of helmet shells were produced. This was accomplished through several steps of press-forming or hot-stamping the shells. The lot number serves as a control number for the manufacturer and as an extra stamp of approval.
 

Manufacturing stamp from the Quist factory, Q64. The number 64 represents the number of centimetres around the edge of steel shell. This number can vary from 60 cm to 70 cm (there are some examples known which are even bigger). The Quist factory primarly manufactured M35 and M40 models however an extremely small number of M42s have been observed.

SE64 - Sächsische Emailler-und Stanzewerke, Lauter (later hkp). Manufactured M35, M40 and M42.
 

The SE factory used the ordnance code hkp as the war progressed. This hkp stamp is from an M40. The stamp is placed on the left inner skirt.

NS - Vereinigte Deutsche Nickelwerke, Schwerte. Manufactured M35, M40 and M42.

EF - Emaillerwerke A.G. Fulda. Manufactured M35, M40 and M42.

The head of a brass rivet. Note the shape of the head with a more domed (higher) profile. The zinc coating has partly chipped off taking with it the paint. During wear, the rivet heads often lost the coating and the overlaying paint didn’t adhere well to the rivet head’s surface.

The flat head of a brass rivet. The coating and paint have chipped off.

The domed head of a rivet still having some zinc coating. This rivet is on an early M35 and may actually be aluminum. Note the remnants of whitewash paint around the head.

Steel rivet with zinc coating on an M42. Note the textured paint around the head.

Flat-headed steel rivet.

Flat-headed brass rivet with zinc coating.

Steel rivet. Note all the paint has chipped of. Rust spots.

2 split rivets from D & C - Dransfeld und Company, Menden, the most common rivet manufacturer. To the left an aluminum rivet dated 1939 and to the right a brass rivet dated 1938.

A brass rivet marked S C and dated 1939. Note the pine tree insignia used by the manufacturer Schmöle und Company, Menden.

Steel split rivet with zinc coated slotted washer. Unmarked.

Late split rivet marked B & C, Beidermann und Czarkinkow, Berlin. Dated 1944.

2 slotted washers. To the left a zinc coated steel washer, to the right an aluminum washer.