This is single tail piece stud, available in either metric or imperial thread, aluminium of zinc, and available in Black, Chrome, Gold or Nickel

Bushing Spec
Width - 12mm (at the knurled section), 11.5mm at the smooth section, 14mm at the lip
Length - 21.5mm (1.5mm Lip, 11.5mm At the knurl, 8.5mm at the smooth)
Material - Zinc
Weight - 9g

Post Spec
Thread - M8 x 18mm (coarse)
Material - Zinc
Weight - 13.6g
Total Length - 33.7mm

Top section of post
Length - 14.4mm (5.4mm top, 1.3mm bottom, central section 7.7mm)
Diameter - 12mm Top and bottom section, 7.6mm middle section