Gateron Black Ink V2's are from Gateron's premium line of switches. They feature a unique housing material and coated spring.  These switches are highly regarded within the community, and arguably one of the smoothest linears. 

Switches are sold in packs of 10.
Quantity 1 = 10 switches. 
Specifications:
Lubed With Krytox 205G0
Linear
4.0mm travel
60g actuation / 70g bottom out
Transparent housing
5 pin