Singer 3323/3321 sewing machine screw size
M4 / M6 · 6 to 10 mm long
Singer 3323/3321 sewing machine takes M4 and M6 metric screws in lengths from 6 to 10 mm.
There are 2 separate fitment records for it, including set screw (M4x6 C) on arm shaft balance (M4) and set screw on free arm foot assembly (M6).
Head and drive, as the sources state them: set screw (headless) head.
2 of the 2 records are marked confirmed, drawn from 1 source (smscanada.com).
For reference, M4 is 4 mm across the threads at 0.7 mm pitch. The imperial size people confuse it with: #8-32 (4.17 mm) — the standard US PC/rack screw, close but not the same.
Singer 3323/3321 sewing machine screw specifications
One row per fitment record. Head, drive are shown only where the source states them; pitch is the ISO coarse pitch for the thread.
| Thread | Length | Pitch | Head | Drive | Where it goes | Status |
|---|---|---|---|---|---|---|
| M4 | 6 mm | 0.7 mm | Set screw (headless) | not stated | set screw (M4x6 C) on arm shaft balance | Confirmed |
| M6 | 10 mm | 1 mm | Set screw (headless) | not stated | set screw on free arm foot assembly | Confirmed |
Fitment records and sources
set screw (M4x6 C) on arm shaft balance
pitch 0.7 mm · tap 3.3 mm · clearance 4.5 mm · PH2 / Torx T20
set screw on free arm foot assembly
pitch 1 mm · tap 5 mm · clearance 6.6 mm · PH3 / Torx T30
How to check the screw before you buy
- Check the strength class stamped on the head (8.8, 10.9, A2-70) and replace like for like.
- Diameter: across the threads an M4 screw measures about 4 mm with calipers (usually a hair under). This device also uses M6, so measure each screw rather than assuming they match.
- Pitch: 0.7 mm from one thread crest to the next (14.29 crests per centimetre). A thread pitch gauge or the pitch-gauge tool settles it in seconds.
- Length: for set screw (headless) screws, measure from under the head to the tip (countersunk heads are the exception: they are measured overall).
- The records span 6–10 mm, which means different positions take different lengths — match each hole to its own screw.
- Driver: the source does not name the drive. Standard M4 heads take PH2 for Phillips and T20 for Torx, and a 3 mm hex key for socket heads; a bit that fits loosely will cam out and strip the head.
- Tightening: no device-specific torque is published in these records. The site's general figure for M4 is about 2.0-3.0 N·m into metal threads and 0.8-1.4 N·m into plastic bosses; snug it up and stop.
Common mix-ups with M4 / M6
- US-made pinball machines (Williams/Bally/Stern) overwhelmingly use imperial UTS threads (#6-32, #8-32, #10-32); explicit metric threads only appear on newer/import components such as Jersey Jack Pinball's Hobbit Smaug assembly (M3).
- Water heater elements use pipe threads (NPSM/NPT), not metric machine screws.
More in Industrial & Machinery
The same screw also fits
Devices whose records share a thread with Singer 3323/3321 sewing machine, closest length match first.
- Needle plate screw for Bernette/EverSewn/Necchi/Singer industrial-style sewing machines also M4 × 6 mm
- Singer 4423 / Necchi / Bernette / EverSewn sewing machines also M4 × 6 mm
- Makita GB801 also M4 × 6 mm
- Singer Viking Emerald 203 sewing machine also M4 × 6 mm
- Avid CNC Laser Kit also M4 × 6 mm
- Diebold Nixdorf DN100 nylon screw also M4 × 6 mm
- Meccano boxed sets (modern metric era) and compatible parts also M4 × 6 mm
- DIN 41612 backplane / rack card retention also M4 × 6 mm
Questions about Singer 3323/3321 sewing machine screws
- What size screw does Singer 3323/3321 sewing machine use?
- M4 × 6 mm for set screw (M4x6 C) on arm shaft balance; M6 × 10 mm for set screw on free arm foot assembly.
- How long are the screws in Singer 3323/3321 sewing machine?
- The records range from 6 to 10 mm depending on the position, so match each screw to its own hole.
- What is the thread pitch of an M4 screw?
- 0.7 mm (coarse), which is the standard pitch for M4 machine screws; a 0.5 mm fine pitch exists but is uncommon. The tap drill is 3.3 mm and the normal clearance hole is 4.5 mm.
- What screwdriver do I need for Singer 3323/3321 sewing machine?
- The sources do not name the drive. For M4, Phillips heads normally take PH2 and Torx heads T20; socket heads take a 3 mm hex key.
- Can I use an imperial screw instead of M4?
- No. Imperial look-alike: #8-32 (4.17 mm) — the standard US PC/rack screw, close but not the same. Use a true M4 screw so it does not cross-thread or strip the hole.