API 5B 5.6 & 5.7 REQUIRE BUTTRESS FORM INSPECTION

Per API 5B 5.6, Buttress Thread Form "shall conform to .. the requirements of tooth thickness or groove width".

TW-6001 Thread Groove Width Gage Inspecting a Part

Tooth thickness is now a required, mandatory element to be inspected.

Why is it required?

API buttress threads are governed by the Specification 5B. The Sixteenth Edition has made some major changes, including mandating the inspection of tooth thickness (either the actual tooth thickness or shave). 5.6 and 5.7 describe the inspection requirements and procedures. Figures 2 and 3 provide the Buttress Casing Thread Form and Dimensions. Table 2 provides the tolerances for buttress dimensions. Also see Table 2 note h, which states "These tolerances apply to the basic .100 tooth width as measure with the single dial buttress thread form gage[.]"

5.6.4  "For buttress threads, the thread form shall conform to the basic dimensions ... including the requirements of thread height, included flank angles, tooth thickness, or groove width."

5.6.4 "The following are examples of acceptable methods of measuring tooth thickness: single dial gauge, optical comparator, contour measuring machine, or cast molds."

Figure 2 Buttress Casing Thread Form and Dimensions

Table 2 defines the Tolerances on Buttress Casing Thread Dimensions

Table 2 note h "These tolerances apply to the basic .100 tooth width as measure with the single dial buttress thread form gage[.]"

What is Tooth Thickness vs. Groove Width?

A single pitch is the combination of tooth thickness (sometimes also called "tooth width") and groove width.

The tooth thickness is the physical helical ridge constructed by the stab flank, load flank, and the crest on a thread screw. The variance in tooth thickness is commonly referred to as shave as measured closely to the pitchline .

The groove width is the physical helical valley constructed by the stab flank, load flank, and the root of a thread screw.

The tooth thickness and groove width have an inverse relationship with each other. If the tooth thickness is narrow, the groove width will be wide, and vice versa.

5.6.4  "For buttress threads, the thread form shall conform to the basic dimensions within the tolerances of Figure 2 and 3 including the requirements of thread height, included flank angles, tooth thickness, or groove width."

How do I inspect it?

5.6.4 allows for the inspection via a single dial gauge. 5.7 describes the type of gauge and procedure to be used. The gage inspects "actual tooth thickness (amount of shave) of both external and internal buttress casing threads near the pitch line." For this

What is Groove Width?

Groove Width GO/NO GO Gages- Form