These were purchased from Kitt Peak, as originally specified by J Mould. They have flat-topped profiles and are intended for use with CCD detectors (unlike earlier filter systems). Three sets exist, all are normally kept in the INT filter store cupboard. The original specifications are given below:
All filters to be 5cm 
5cm, 3mm thick, blocked to 1.1 micron, better than 75%
peak transmission (except B 70%), MgF
coated, no pinholes, optical quality
glass.
R: Filter 7200Å = short-pass hard-coated on 3mm OG590, blocked to 1.1 micron,
75% or better peak transmission, MgF
coated on glass side.
I: Filter 9000Å = Short-pass hard-coated on 3mm RG-M9, blocked 1.1 micron,
75% or better peak transmission, MgF
coated on glass side.
V: Filter 6000Å = Short-pass hard-coated on 3mm GG 495 blocked to 1.1 micron,
75% or better peak transmission, MgF
coated on glass side.
B: Filter 4900Å = Short-pass, hard-coated on the glass substrate indicated below, blocked to 1.1 micron, 65% or better peak transmission, MgF2 Coated on glass side. Glass substrate to be cemented combination of Schott GG 385 and either Hoya GM-500 or Hoya C-500 (whichever will adequately suppress the red leak). Total thickness to be 3mm as with the other items.