High Quality:
Quantity: 6
M6 x 1 thread commonly used on fins. Bronze Barrel Nuts for windsurfing fins and foils
9.0 mm diameter, 15.8 mm long.
Material: sea water corrosion resistant Bronze C952. This Bronze is  the high price Bronze used for cargo ships propellers due to resistance to corrosion and high strength. C952 is the best corrosion resistance and strength Bronze available for marine applications.

Shipping:

USPS - free but unreliable. 1 out of 50 packages delivered 1-4 weeks after estimated by eBay.

UPS - $9 flat rate. Delivers every package as promised on the listing or faster.

UPS 2nd Day Air- $20 flat rate. Fast and reliable. 

UPS Next Day Air - $40 flat rate. The fastest and reliable.

On UPS shipped orders I take extra steps to improve surface finish well beyond the item description.