You are looking at one Pro-tek CNC billet brake fluid cap that replaces the stock plastic Rear Brake Fluid Master Cylinder Reservoir Cap on a 1998-2006 Suzuki Katana 600 GSX600 and 1998-2006 Suzuki Katana 750 GSX750 models.
This one cap comes available in 4 brite dipped anodized colors -red, blue, gold and silver.
This reservoir cap is made from 6061 T6 billet aluminum, is brand new still in original packaging, manufactured in the USA, and comes complete with manufacturer warranty.
This round threaded rear brake fluid reservoir cap (Pro-tek Part No. RC-100) is 2.25" x .50" and has the word Pro-tek engraved on it twice.
The retail price for this cap is $25.
These are not "NO Named Brand" cast aluminum caps machined later to look like billet (made in China) that are all over the Internet. These are American made from solid billet aluminum, 100% CNC machined from a name you can trust - Pro-tek - a leader in the motorcycle industry for over 25 years.