This is an excellent Royal Scots Fusiliers (RSF) Pipers Waist Belt Clasp

This is an excellent Royal Scots Fusiliers (RSF) Pipers Waist Belt Clasp. 

Regiment: The Royal Scots Fusiliers (21st Regiment of Foot), designated a Royal regiment in 1713 and a Fusilier regiment (elite infantry) in the late 17th century.

Item: Pipers/Officer's Waist Belt Clasp (WBC). Pipers and officers of Highland/Scottish regiments wore highly decorative silver or silver-plated clasps on their full-dress belts. The size (4" x 3") and weight confirm it as a main belt ornament.

Design & Date (Post-1877 Victorian):

Silvered Metal: A common and high-quality material for Scottish military accoutrements.

Quatrefoil Shape (4" x 3" with lobes): The four-lobed or quatrefoil shape is classic for many Scottish waist belt clasps.

Central Strap/Motto: The circular strap with "THE ROYAL SCOTS FUSILIERS" identifies the regiment.

Flaming Grenade with Thistle: The flaming grenade is the traditional badge of all Fusilier regiments. The inclusion of the Thistle on the grenade's ball is a unique distinction of the Scottish Fusiliers.

Four Prince of Wales' Feathers: This is the key detail that places the badge's design specifically to the post-1877 period. The RSF had this honour added to their badge around the time their regimental title changed to include "Royal Scots Fusiliers" in 1877. The Prince of Wales' feathers are seen at the four corners of the clasp, over the thistle sprays, signifying the regiment's royal association and the honorary title of their Colonel-in-Chief.

This is indeed a scarce item, representing the full-dress regalia of a distinguished Scottish regiment from a specific and important period in British military history.