I'm building this frame from the ground up:

https://www.deitycomponents.com/cryptkeeper_frame.html

The specs for the headset say:

• IS 52/40 Lower Bearing (Tapered Steerer)
• IS 52/30 Lower Bearing (Straight 1 1/8" Steerer)

In my research, I've found that IS stands for INTEGRATED ANGULAR CONTACT.

My fork is a manitou circus expert (which has a tapered head tube)...

What exactly do these specs this mean? Is the "52/40" a specific measurement?

I'm building this frame from the ground up:

https://www.deitycomponents.com/cryptkeeper_frame.html

The specs for the headset say:

• IS 52/40 Lower Bearing (Tapered Steerer)
• IS 52/30 Lower Bearing (Straight 1 1/8" Steerer)

In my research, I've found that IS stands for INTEGRATED ANGULAR CONTACT.

My fork is an 2014 Manitou Circus Expert (which is tapered)...

What exactly do these specs this mean? Is the "52/40" a specific measurement?