I am looking at a company-written standard for cast parts. The castings are blanks for driveshaft yokes, similar to what is pictured below. The standard defines general tolerances for the dimensions on the part, and it classifies them into two categories:

  1. Outside dimensions and center-to-center distances
  2. Inside dimensions (core dimensions) 1

There is some confusion between us and our supplier as to what constitutes an inside dimension. Obviously, anything that requires a core (such as pilot holes for the yoke ear holes seen below) will be an inside dimension.

However, when our internal inspection requirements were laid out, things such as the distance from inside edge to inside edge of the ears were determined to be inside dimensions, while the outside edge measurement on the ears is an outside dimensions.


First, is this terminology common to castings (or even forgings) in general? I have looked at ISO standards regarding general tolerances, but they make no reference to it. If it is common, are inside dimensions strictly related to features requiring cores? Should other dimensions be considered "inside"?

For reference, the tolerances for outside dimensions are asymmetrical, with the high end being larger than the low end (e.g. +1.0/-0.5), and the inside tolerances are symmetrical to the same absolute value as the low end of the outside dimensions (e.g. +/- 0.5 to match the first example).

1. This is verbatim how it is listed in the standard.

  • $\begingroup$ Are you relying solely on written specifications for your tolerance? It seems that a drawing with tolerances and dimensions should clear it all up. $\endgroup$
    – hazzey
    Commented Dec 15, 2015 at 17:53
  • $\begingroup$ These drawings have some specific tolerances, but a lot of the dimensions are left to fall back on the general tolerance. It's just that instead of calling out something international like ISO 2768, these castings refer to an internal standard we send out to suppliers as necessary. $\endgroup$ Commented Dec 15, 2015 at 17:58
  • $\begingroup$ And to preempt the notion that we clarify these specific dimensions on the drawing, these parts are drawn and controlled by our German division who uses a different supplier and is not having this issue. $\endgroup$ Commented Dec 15, 2015 at 17:59
  • $\begingroup$ So, if I'm understanding correctly: Your company wrote a standard and asked your supplier to conform to it. Your company's supplier is claiming there is an ambiguity in that standard, where your company assumed the language was clear. According to your company's interpretation, the tolerances on the ears are - just guessing here - more strict than in the supplier's interpretation? Do some of the supplied castings conform only under one party's interpretation, or am I leaping to an unwarranted conclusion here? $\endgroup$
    – Air
    Commented Dec 15, 2015 at 23:57
  • 2
    $\begingroup$ I ask because if the interpretation is moot with respect to whether delivered parts meet the spec or not, it seems like the solution here is simply to revise the specs to remove the ambiguity, in whichever way your company pleases. $\endgroup$
    – Air
    Commented Dec 15, 2015 at 23:59

2 Answers 2


As a cast part, there should be at least two pieces that form the mold. There should be parting line between these pieces. Dimensions on one side of the parting line would be considered outside dimensions while dimensions on the other side would e considered inside. If the parting line is not specified on the print, then it could indeed be ambiguous as the part may be possible to cast with the parting line on different sides of the feature. If this is the case then the drawing should be revised.


Based on surface texture, it looks like this might be a sand casting. That said, I'm not familiar with the distinction between inside and outside dimensions. We do commonly differentiate between dimensions that cross a parting line and those that don't. The ones that cross a parting line have a greater tolerance.

Is an inside dimension one that's formed by a core, or is contained completely on one side of the mold? I'm definitely interested for my own reference.


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