Iso 8015 ((link)) Page

Actually, the old default was the "Envelope Requirement" (Taylor Principle). ISO 8015 did something radical: It said that . That is, each specification on a drawing stands alone . A size tolerance does NOT control form unless explicitly stated. A flatness tolerance does NOT control parallelism unless explicitly stated.

Then came a quiet revolution from Geneva, Switzerland. Its name was . The Old Way: The Silent Assumption Imagine a French aerospace company in 1985. An engineer drafts a simple shaft for a landing gear actuator. He specifies a diameter of ( 50 \pm 0.1 ) mm. He does not specify straightness, roundness, or parallelism. Why would he? The old default said: If no geometric tolerance is given, the size tolerance controls form . This was the Taylor Principle (or Envelope Requirement). The perfect virtual cylinder of the maximum material condition (MMC) would automatically limit how bent or oval the shaft could be. iso 8015

But the real victory came in global supply chains. After ISO 8015 was widely adopted (revised in 2011 as ISO 8015:2011, and eventually absorbed into the GPS master standard ISO 14638), a drawing from Japan could be read identically in Brazil, Germany, or South Africa. The standard eliminated the "translation errors" that had cost billions in scrap. Actually, the old default was the "Envelope Requirement"

But here’s the rub: That default only worked for features of size (holes, shafts). What about a flat surface? No default. What about the angle between two faces? No default. Every drawing was a minefield of unspoken agreements. Japanese suppliers assumed one set of defaults; German suppliers another. When a part arrived from Italy and failed assembly, the argument wasn’t about the part—it was about which standard applied . A size tolerance does NOT control form unless