A Silver coloured brass belt buckle, with prong and clasp.  The internal width (the size of the strap/webbing you would use), is 25mm.  

This is a non-sew clasp which was patented in the UK around 1952.  It's an easy to apply little buckle, simply slide a 1" wide piece of leather strap under the moveable clamp on the back (the reverse of the belt will be uppermost when doing this.  Then slide the clamp to secure.  No sewing required, just add a few holes to your belt and away you go!

The actual manufacture date of this particular stock is unknown, but the original company pretty much ceased trading around 25 years ago.

Here's a bit of history for you!

THOMAS WALKER (FASTENERS) LIMITED Company number 00626475

 https://worldwide.espacenet.com/patent/search/family/010237168/publication/GB669432A?q=669432

Patent  

Improvements relating to buckles for belts, bands, tabs and the like

GB669432A • 1952-04-02 • 

WALKER LTD THOMAS

Earliest priority: 1949-10-11 • Earliest publication: 1952-04-02

Applicants

WALKER LTD THOMAS; THOMAS WALKER; HERBERT HOWARD WOOD

Classifications

IPC

A44B11/00;

CPC

A44B11/008 (EP);

Priorities

GB2602549A·1949-10-11

Application

GB2602549A·1949-10-11

Publication

GB669432A·1952-04-02

Published as

GB669432A

EN

Improvements relating to buckles for belts, bands, tabs and the like

Abstract

669,432. Buckles. WALKER, Ltd., T., WALKER, T., and WOOD, H. H. July 7, 1950 [Oct. 11, 1949], No. 26025/49. Class 43. [Also in Group XXV] A buckle is secured to a belt or the like by clamping the fixed end 14 of the belt between a member e.g. a plate 4, attached to the buckle, and a cross bar 11 of a slidable clamping element 5, said cross bar having bent ends provided with inturned lugs 13 which are slidable over inclined parts 9 of the plate 4. A rectangular plate 4 having cranked inclined sides 9, has one end hinged to the end bar 3 of a pronged buckle 1, and at the other end has a flattened loop 7 by which the usual belt-retaining loop 8 is fixedly secured. The lugs 13 may be provided with projections or teeth to engage grooves 10 formed in the ramps 9. The edges of the clamping bar 11 are provided with teeth 12 to bite into the belt. The two ramps 9 may be replaced by one broad wedge-shaped part. The invention may be applied to a box-type buckle wherein a plate is pivoted between the flanges of a front cover and provided with a part for securing the free end of a belt against the inner face of said cover, the said plate being also provided with clamping means as above for securing the fixed end of the belt.

Front-page drawing from GB669432A