How to interpret running fit limits per ASME B4.1

[ssylvest]

I need some help understanding how to interpret the limits of clearances shown in Table 5 of ASME 4.1 "Preferred Limits and Fits for Cylindrical Parts". For a 5.50" diameter pin (forming a hinge pin that goes into a bushing), with a Class RC 7 fit, it appears Table 5 indicates the ID of the bushing should be from 0 to 4 thousands of an inch over, and the pin should be between 6 to 8.5 thousands of an inch under.

But what do the two numbers to the left mean, under the column "Limits of Clearance" which are 6.0, and 12.5?

Does the RC7 fit sound like a logical and practical choice for my intended application, for fabricated hinges on flood gates (Stainless Steel pin in a bronze bushing, with grease fittings) that will be used once every few years as a storm arises? My typical role is the structural design of the carbon steel elements, so this type of hinge specifications are somewhat unfamiliar to me.

 

[Mekada]

Limits of clearance means you will always have a clearance between 6 and 12.5 thousands of an inch. (0 over + 6 under = 6 clearance, 4 over + 8.5 under = 12.5 clearance)