Parson's Sloper Telephones

[wurzel1765]

Here are some Parson's Sloper phones from my collection I thought you might like to see 

[.....]

Very nice, never seen this type before. Interesting.

[HarrySmith]

Very cool! What year(s) are these from?

[wurzel1765]

they're from the 1920's

[countryman]

It looks like they're more house intercoms, or could they be switched to office lines? Nice phones indeed, thanks for sharing

[FABphones]

Parsons-Sloper. 'Interphones'.

Found this short thread from 2011:
http://www.classicrotaryphones.com/forum/index.php?topic=4797.0

And these catalogue/advertising images from the internet.

ETA:
'1872 - John Thomas Gent started the business after serving an apprenticeship in Halifax.
It is said that G.T. Gent and Co were one of the first to produce electric bells in the UK. During the first years Gent was interested in developing electrical equipment, including telephones, fire alarms, electric lightning and other devices.
1884 - I.H. Parsons was apprenticed to Mr Gent, later followed by A.W. Stavely.
Mr Gent retired from Gent and Co that year, leaving Parsons and Stavely as joint partners'.