These are Nuts & Nipples t/s 3/8 Pipe and are supplied in bags of 5. 

Either: 

5x 9/16 x 26tpi Nuts

5x Flat Nipples

5x Cone Nipples 

5x Nuts + Flat Nipples

5x Nuts + Cone Nipples

Just Added exclusively for JRME: 

5/16 Pipe reducing nipples to suit 9/16 x 26 nuts. These are available in the same quantity's as above.

These are manufactured items, so please allow up to 7 days for delivery.