The 451 is the 65 mm (2-1/2 in) double-edged straight carbide blade that comes on the Bahco 665 Ergo Scraper, sold on its own as a replacement.
The 665 is Bahco's heavy-duty, two-handed scraper for power scraping large areas. With two cutting edges, the 451 can be turned around when one wears. The 665 also takes the 50 mm 442 blade.
Bahco traces back to 1886, when Johan Petter Johansson founded a mechanical workshop in Enköping, Sweden. He invented the modern pipe wrench in 1888 and patented the adjustable wrench in 1891. The Bahco name comes from B.A. Hjorth & Co., the firm that sold his tools, and the brand is now part of Snap-on.