A good quality Longcase or Grandfather clock double ended suspension spring. Used at the top of the pendulum, which flexes allowing the pendulum to swing freely.
Manufactured in the UK from hardened and tempered high carbon spring steel strip.
Strip dimensions, 0.15mm x 6.27mm x 98mm long
Block dimensions 3/8″ x 3/16″ (9.47mm x 4.75mm) drilled and threaded 5BA .