Two different things both called "threads" in SolidCraft
Search the UI for "thread" and you'll land in two places that do different jobs:
- Hole (H), Tapped option — makes a hole, then optionally tags its wall with thread metadata (metric, UNC/UNF, or G/Rp) and a matching tap-drill size. This is what most people actually want: a bore sized so a real-world screw or fitting goes in.
- Thread (
solid.thread) — a separate command for putting thread metadata on a cylinder you already modeled, rather than cutting a hole. It's ISO metric only.
Neither one carves a helical groove into the part by default. Both store a designation (like M8 or 1/4-20 UNC) and geometry stays a plain cylindrical bore or cylinder. If you need a part that actually looks threaded in a render or 3D print, you model that separately with a swept cut — these two commands are for callouts and drill sizing, not thread-profile geometry.
What the Hole catalogue actually covers
The Tapped option in the Hole dialog gives you:
| Family | Sizes | Profile | Notes |
|---|---|---|---|
| ISO metric | Coarse catalogue + 15 extra fine diameter/pitch pairs | 60° | Pitch isn't shown in the designation for coarse (M8), but is for fine (M8x1) |
| UNC | 14 sizes, #4–#12 and 1/4"–1" | 60° Unified | Designation like 1/4-20 UNC |
| UNF | 14 sizes, #4–#12 and 1/4"–1" | 60° Unified | Designation like #10-32 UNF |
| G / BSPP (internal) | 1/8" to 1", 6 sizes | 55° parallel pipe | BSPP accepted as an alias for G |
| Rp (internal) | 1/8" to 1", 6 sizes | 55° parallel pipe | Kept as a separate family from G — drill recommendations differ |
The docs are explicit that this is a verified subset, not full coverage of any of these standards — don't expect every size a hardware catalogue lists.
A few things that trip people up:
- Numbered Unified sizes (#4, #6, #8, #10, #12) are nominal screw diameters, not drill numbers that happen to share the digit.
- Pipe sizes like
G 1/4are nominal labels — the actual basic major diameter of G 1/4 is 13.157 mm, not 6.35 mm. - The modeled geometry is always a straight cylindrical pilot bore with cosmetic metadata attached — no tapered thread (like NPT) is represented, because that would need a cone, not a cylinder.
Where the suggested drill size comes from
| Family | Method | Source |
|---|---|---|
| ISO metric | Nominal diameter minus pitch, rounded to 0.001 mm (M8 → 6.75 mm) | Existing SolidCraft convention, unchanged |
| UNC / UNF | Guhring's "approximately 75% theoretical thread" cut-tap column | Guhring, Tap Drill Sizes |
| G / BSPP, Rp | Yamawa's drill column (default) + a separate recommended process-bore figure | Yamawa YEU23 European catalogue |
These are cutting-tap starting points, not form-tap recommendations, and SolidCraft's own docs say material, hole depth, drilling accuracy and your tap manufacturer's process guidance still determine the drill you actually use. If you type in an explicit diameter, that overrides the suggestion.
For G and Rp specifically, SolidCraft shows two different numbers on purpose — a drill size and a process-bore recommendation — because the two pipe-thread families use different drills even at the same nominal size. The six catalogue pairs, in mm:
| Nominal | G drill | Rp drill | G process-bore | Rp process-bore |
|---|---|---|---|---|
| 1/8 | 8.75 | 8.5 | 8.78 | 8.55 |
| 1/4 | 11.75 | 11.4 | 11.78 | 11.5 |
| 3/8 | 15.25 | 14.8 | 15.28 | 14.9 |
| 1/2 | 19.0 | 18.5 | 19.04 | 18.55 |
| 3/4 | 24.5 | 24.0 | 24.52 | 24.1 |
| 1 | 30.75 | 30.2 | 30.77 | 30.25 |
Turning on cosmetic thread markings
By default, a tapped hole or Thread feature looks like a plain smooth bore in the viewport — the thread only exists as metadata until you turn on the display:
Preferences → Graphics → Cosmetic thread markings
What that switch does and doesn't do:
- Applies immediately, no rebuild, no camera move needed.
- It's an application preference, not a document property — turning it on doesn't change the saved file, and it has no effect on exported mesh/STL/STEP data.
- Draws schematic, slightly tilted bands on the threaded cylindrical wall, for both internal and external threads, using the thread's stored metadata including partial length.
- Only shows in the shaded desktop and web viewport. Wireframe mode and transparent/faded bodies don't get it — SolidCraft's depth-tested line pass can't represent a faded body's visibility correctly, so it's left off there rather than drawn wrong.
- Band count scales with pitch, up to 32 bands per feature, scaling down to as few as 4 as a scene gets denser, inside a shared budget (500,000 inspection units, 65,536 total strokes, 32,768 per body). Big assemblies can lose later markings to that budget; it's not a bug if a distant small hole shows no bands.
- It's purely visual. There's no major-diameter entry circle and this isn't a thread-inspection or dimensioning tool — if you need to check an actual thread dimension, that's a separate measurement, not something the marking itself reports.
FAQ-style notes worth knowing before you model
- Coarse vs. fine metric designation:
M8always means the coarse pitch (1.25 mm) and the pitch is left out of the label; any fine or custom pitch is always spelled out, e.g.M8x1. This is a labeling convention only — it doesn't change the resolved pitch or the actual hole geometry. - Custom sizes stay custom: pick Custom in ISO metric, type your own diameter and pitch, and the dialog keeps Custom selected even if your numbers coincidentally match a catalogue entry.
- G and Rp are not interchangeable in the UI or in the recommended drills, even though they describe geometrically similar parallel pipe threads — the docs call this out explicitly so you don't copy a G drill size onto an Rp hole.
As always, build small test geometry before committing to a production part: make a plate, add a Tapped hole, try a few sizes across families, save, reopen, and confirm the designation and drill size you expect are the ones you get.