Vintage Technology: Metal Puzzles

Who didn't have these as a kid and loved twisting and turning them?  A guide to the UK's most popular brands with solutions and analysis of the geometry.

The metal puzzles are broken down into various types:

Type 1: Twist and separate.  Simple separation by aligning two gaps at 90 degrees.  The shapes can consist of crossed-circles, fluted-circles, L-shaped loops, triangles and paper clips but the idea is the same.  Variations include long-armed circles and triple combinations.
Type 2: Locked-in shapes.  A smaller shape is locked in by a larger, but not large enough shape.  Often released by passing through the end of the retaining piece.
Type 3: Keyhole manoeuvre.  Use one piece through another to (easily) navigate through the lock.
Type 4: Twisted manoeuvre:  Variation on the Type 1 puzzle that involves multiple twisting to eventually unlock a simple shape from a spiral or align two different pass-through parts.
Type 5: Maze: Involves going through a series of positions, in a particular order to eventually separate the parts.

...and the various brands.

Merit: UK company that issued a range of puzzles of quite high quality, if limited variation, by J&L Randall Ltd.
International Card Company: Formed in 1903 and taken over by de la Rue in 1919 to be renamed Gibson Games (aka HPG).  Early products were mostly card-based.
HPG: H.P.G & S Ltd (aka HP Gibson & Sons Ltd, aka Gibson Games).  UK (London) company that was founded in 1919 and still around today making jigsaws and games.
Chad Valley: Game company since 1860 that is still trading to this day.  They were an early innovator of creating links with TV - such as The Sooty Show and bought by Palitoy (the creator of the MB games brand) in 1978.  However, these days they specialise in toys for children from pre-school to ten years old and is exclusive to the UK department store Woolworths - as it is owned by them (since 1988).