old buckle need help Iding

[BOXING63]

Hello everyone need help Iding this buckle...and how to clean it, it measures 3 3/4 x 3 1/2 Thank you

 

[BOXING63]

Thank you

 

[TheCannonballGuy]

It appears to be a horseharness buckle. It is very similar to a halter-square, but yours is larger. Our fellow TreasureNet members Creskol and BosnMate are experts at horse-&-wagon harness gear, so I hope will speak up with your buckle's specific ID.
Halter Square: Equestrian | eBay

You asked about how to clean it. The method used by most relic-diggers for removing the thick rust-encrustation from iron is called Electrolysis. Here are instructions:
Cleaning Shells
An alternative ironcleaning method which doesn't use electricity is the Zinc-&-Lye-Bath process:
Cleaning Iron Relics

Contrary to some instructions, the best clear-coat to apply to iron relics after cleaning is Polyurethane, NOT paint or lacquer, because unlike those coatings, Polyurethane is a true Oxygen-proof Sealant. I use MinWax Fast-drying Polyurethane spray, Satin Finish version (not the Gloss version). It is available at Wal-Mart for $7.29 per spraycan. I typically apply 3 or 4 "moderate" coats of Polyurethane. I said "moderate" because you don't want to spray too heavily, which causes drips-&-runs to form -- but you also don't want the coats to be too thin. I apply each successive coat about 20 minutes apart.