The 6 bolt helmet was the most popular with divers. On 12 and 8 bolt helmets, 4 brailles were needed. 
With the 6 bolt helmet only 2 were needed. The chance of ripping the collar on the suit became a lot smaller this way.
Photo courtesy of Leon Lyons.

Used condition
 

6 bolt Admiralty pattern helmet has a 4 1/2 inch diameter face glass which is 1/2 an inch thick.
The spitcock on the divers left side can be operated by the diver's right hand.
 

The side view shows the weight lug and the outlet or exhaust valve which is located to the rear of the diver's right ear.
The rear view shows the air inlet valve with a non-return valve fitted and the telephone connector gooseneck.
There is a small stop pin to the back of the helmet which prevents accidental unscrewing of the helmet from the breastplate.

Photos courtesy of Jan Hasselbach
 

A nice Jake!

A rare find! A Siebe Gorman helmet with hinged front window....
 

Here is another 6 bolt hinged window helmet . The spitcock on the diver's right hand side is an unusual design, operated by a wheel.
There is a reinforced patch of copper riveted on the crown of the helmet. This was added to strengthen the top of the helmet.
Divers working on ship's bottoms were often subjected to knocks on the helmet and denting often occurred.
By adding the reinforment to the top of the helmet the life of it would be extended.
 

Here is another 6 Bolt helmet with a hinged window. The spitcock is on the left hand side of the diver.
This was the preferred position on later helmets. This helmet was owned in its working life by Antonius Muller from Holland.
It was used by Antonius whilst working for the Rikswaterstaat in Holland on projects such as the Moerdijk and the Zaltbommel Bridges.
 

Here we have 3 pictures of Antonius at work with one of his helmets.

Photos courtesy of the Clint Green Collection.

Especially for the Royal Dutch Navy the standard hat was fitted with a top light and an extra air inlet on the corselet for safety. The chest weight was replaced with a air-chest weight from the Draeger company. You can see in the picture that the nipples were replaced with hooks. The diver was able to let air in via the corselet. In case of an emergency he could even cut the hosepipe and go up on his own air-supply.

Another engineers helmet, Picture contributed by Raymond Dupont.

A Royal Dutch Engineers helmet with a difference.
This one is fitted with an unidentified inlet just below the air inlet elbow.
Otherwise it is the same as the usual pattern.

Here is helmet 19443. It is one of the latest
6 bolt helmets that left the Siebe Gorman factory.
Notice the nametag. It is the one but latest style. The latest style
can be found at the end of the Siebe Gorman 12 bolt section.

This helmet was bought in Bogata in South America from
an aluminium door and window company. It was bought
for the scrap metal value in the early 1980s.

Photo courtesy of RJ Timmerman - Nebraska.