Thread data & callout resolver
An M8 × 1.25 – 6H nut has a pitch diameter of 7.188–7.348 mm and a minor diameter of 6.647–6.912 mm, cut with a 6.8 mm tap drill: the thread the tool below opens on. Type a callout, or choose a size in the callout’s own boxes, to open either member’s limit dimensions, class and tap drill, each resolved per the governing standard.
Type the callout as the drawing prints it (M10x1.5-6g, 1/4-20 UNC-2B, M6X1-6g LH) and the page answers for that thread: its limits, how to make it, how to check it, and what goes on the FAIR.
What do the thread limit dimensions mean?
A thread is toleranced on more than its major diameter. For an external thread (a bolt or stud) the standard fixes the major and pitch diameter limits; for an internal thread (a nut or tapped hole) it fixes the pitch and minor diameter limits. The pitch diameter is where the thread actually fits and carries load, so it is the dimension a thread gauge and a FAIR report care about most.
The class (ISO 6g/6H, Unified 2A/2B) sets how tight that fit is and which way the allowance falls. This page reports the class the dataset holds for each size; alternate classes are not fully enumerated.
How is a thread callout resolved?
A callout such as M6X1-6H LH encodes a family (metric), nominal and pitch (6 mm × 1 mm), a class (6H, internal), and a hand (left). The resolver normalises the text, matches it to a family and tabulated size, and returns the tap drill — the same parse the ASdrawn pipeline runs when it reads a thread note off a drawing. Insert callouts (HELI-COIL, KEENSERT) are flagged as a helical-wire-insert intent on the parent thread.