ScrewSpan - Screw Length Comparator | Two Head References

ScrewSpan is a handheld comparison card for sorting loose screws by length during assembly and repairs. The two stations use different head contact surfaces, so the head is included only when the selected reference calls for it.

Left - UNDER HEAD, nominal 5-60 mm

Hold the card upright, with the labels facing you and the screws pointing downward. Place the shaft in the open V fork. Let a flat underside of the head rest on the TOP of the fork. The head sits in the open clearance window above it. Compare the tip with the left scale. This station is intended for ordinary protruding heads with a flat bearing underside.

Right - TOTAL, nominal 12-60 mm

Place the shaft in the lower V guide. Gently hold the flat TOP of a countersunk head UP against the UNDERSIDE of the upper stop. Keep that contact while reading the tip against the right scale. The head clearance window leaves room between stop and guide. This station is intended for flat countersunk heads; it is not a hanging support.

Dimensions and intended range

110 x 104 x 12 mm overall; 3 mm back plate. Open 90-degree V guides are intended for shafts about 2-6 mm in diameter. Nominal scale marks are 1 mm apart, with longer marks at 5 and 10 mm and raised numerals. Both scales reference the indicated head contact face. The small bottom hole is for storage. No assembly or extra hardware is needed.

Reading the scales

Look straight at the front of the card, keep the screw parallel to the scale and check that its head contacts the correct face. The tip sits forward of the scale, so an oblique view introduces parallax. This is a printed comparison aid for sorting, not a calibrated measuring instrument. Use calipers when the measurement matters. It does not identify diameter or thread pitch, and special fastener length conventions are outside this guide.

Printing

Print the broad flat back on the bed, with guides and lettering upward. Suggested starting point: PLA, 0.4 mm nozzle, 0.2 mm layers, 3 perimeters and 15% infill. The geometry is designed without supports. Choose a profile for your own printer and material; inspect the preview, especially the small scale marks and the V guides. Lightly remove strings or rough contact edges before a real trial. The 3MF contains geometry and placement only. No printer-specific G-code is supplied.

Verification status

The exported STL and geometry-only 3MF were checked independently for a closed single body, dimensions, head-contact faces, open head clearances, V guides and scale positions. Thirty schematic screw/length combinations were checked for 3D interference. Both exports produced actual matching toolpaths with an isolated generic PLA profile, preserving the marks and lettering. These checks do not establish physical fit or measurement accuracy.

Physical printing and use with real fasteners have not yet been tested. Head retention, feel, legibility, printed dimensions, repeatability and accuracy remain unverified. Digital checks and illustrative screw placements are not a physical compatibility test. The images are CAD renders/projections of the exported STL; any screws shown are schematic and are not supplied.

Files

One STL, one geometry-only 3MF in millimetres, original parametric Python source, bilingual instructions and licence. Import at 100% scale. Changes to the source need fresh geometry and slicing checks.

Original CAD design by MARGRAF ITALY. Creative Commons Attribution 4.0 International.

Italiano

Scheda da tenere verticale per confrontare la lunghezza di viti sciolte. A sinistra si appoggia la faccia sotto testa SOPRA la forcella, confrontando 5-60 mm. A destra si tiene la sommità PIANA della testa svasata CONTRO LA FACCIA INFERIORE della battuta, confrontando la lunghezza totale 12-60 mm. Leggere frontalmente per ridurre la parallasse. Ingombro 110 x 104 x 12 mm, monopezzo; stampare il retro piano sul piatto. E un ausilio per ordinare, non uno strumento calibrato. Prova fisica e compatibilita con viti reali ancora da verificare. Le viti nelle immagini sono schematiche.