SPYDERCO DROP-POINT KNIFE S/N406

This knife is a bit of an oddity to me The knife itself is a 3.5' drop-point with a worked/hammered spine stamped SHEFFIELD? There's no crossguard just a brass bolster The grips are light tan micarta pinned onto the tang Now the odd thing about this knife is on both slabs is a SPYDECO button set in the grip? The knife is 8' overall The sheath is black leather with a flap over top stamped 12 GUAGE in a circle The knife is pre-owned and is in good condition S/N406 PRICE includes UK delivery