Convert one engineering value between metric and imperial with shop-floor precision rules. Kinds: length (mm⇄in), tolerance_deviation (a ± deviation, keeps an extra significant digit), geometric_tolerance (GD&T value), surface_roughness (Ra µm⇄µin), weight (kg⇄lb), thread (designation lookup, e.g. "M8" ⇄ "5/16-18 UNC"). Returns the exact value, the display-rounded value, and how it was derived (exact/rounded/table/nearest) with a confidence score.

Convert a printed drawing callout (or short text with several callouts) between metric and imperial, preserving notation: "Ø30 H7" → "Ø1.1811 H7", "84±0.1" → "3.3071±0.0039", "R13" → "R0.5118", "M8" → "5/16-18 UNC", "1/4-20 UNC" → "M6". Angles (°) are left unchanged. Set category=surface to read bare numbers as Ra roughness instead of lengths. assume_lengths=true additionally converts every remaining number as a length (for tolerance-table rows like "bis 30").

Look up the closest standard counterpart of a thread designation (ISO metric coarse ⇄ Unified UNC), with major diameters, pitch/TPI and how close the match is. Omit designation to get the whole cross-reference chart (M2–M30).

Read the printed text tokens of one page of a technical-drawing PDF: each token with its index, text and position (page points, top-left origin, rotation in degrees), plus page geometry and a heuristic guess of the drawing’s unit system. Use the token indices to build classifications for convert_drawing_pdf when you want to decide yourself which tokens are convertible values (e.g. mark a bare "3.2" next to a surface symbol as category=surface, or a title-block number as skip).

Produce a converted copy of a technical-drawing PDF with every recognised value stamped in place (white cover over the original callout, converted text in matching size/rotation) — dimensions, ± tolerances, fit classes, Ø/R callouts, threads. The input file is never modified. Without classifications, a heuristic converts unambiguous callouts plus (by default) bare numbers as lengths; for full control call extract_drawing_text first and pass per-token classifications. Requires a PDF with a text layer — scanned drawings need the web app (https://metric-to-imperial-converter.imnoo.com). Converted values are stamped over the original callouts. Verify safety-critical dimensions before manufacturing use.