Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: What is the inside diameter of the collar in millimeter or inch? Thanks.
Document: The construction of metal was first class with color (off white) being slightly off from lense but not enough to bother me . However the gripe I have is that the padding inside that grips the lense is not thick enough . The camera slides or twists even when locked down . I had to add thicker padding , you also have to face the bottom where it bolts to tripod facing forward otherwise it knocks into battery grip. if you use one.
When you give the knob a half turn to tighten it around the lens, it makes a good, tight grip, and the rubber on the inside of the ring gives good protection for your lens - there's no metal-on-metal contact to speak of. However, be advised that the knob doesn't secure (unless I was doing something wrong) and can easily turn (especially when handholding), slightly loosening the ring. But there is NO DANGER whatsoever of the lens falling.
As other reviewers have noted, the inner liner of this ring is a little sticky and doesn't offer the butter smooth rotation of an OEM Canon ring, but I can live with that to save $150.The ring exactly fits the groove in the lens barrel for both diameter and width. Quality control of the casting and machining process did a good job here.
I won't trust any tripod collar again, even Canon.
Nice smooth inner lining. Solid as can be. I think this works just as well as the more expensive Canon collar.
The  item is compact and of good quality, the color matches perfectly with the lens and  very easy  to  lock/unlock  the lens  from the collar.
Seems to do the job, money well spent. Most probably as good as the Canon collar, and less money. For the price of the lens, Canon should have included a collar making this investment unnecessary.
However, I prefer this issue to one where the grip isn't tight enough! I've had no issues with the screw coming loose but will update my review after I've use the collar for a while longer.
I ordered this item for my Canon 70-300 F4 L series lens...received it in good timeThe collar itself is a good fit and appears to be of good quality materials.
The Canon version of this collar was a great deal of money. I was afraid this was going to be too cheap to risk my new L series lens. I was surprised at how heavy and secure this is. Very pleased so far.
Answer: It's 3 inches and 3/16.