Here are the standard brass tube sizes that will fit snugly either inside or outside 1/8-inch brass tubing:
📏 Basic Dimensions of 1/8″ Brass Tube
- Nominal size: 1/8″
- Typical outer diameter (OD): ~0.125″
- Wall thickness (common): 0.010″–0.014″
- Typical inner diameter (ID): ~0.097″–0.105″ depending on wall thickness
So you want tubing whose OD matches the ID of your 1/8″ tube (for a snug inside fit), or whose ID matches the OD of your 1/8″ tube (for a snug outside fit).
✅ Pieces That Will Fit Inside 1/8″ Brass Tube
Look for brass tube with an outer diameter just under the inner diameter of the 1/8″ tube. Common close fits:
| Candidate Tube Size | Approx OD | Fit |
| 3/32″ brass tube | ~0.0938″ | Good slip-fit inside 1/8″ tubing |
| 0.095″ tube | 0.095″ | Very snug fit inside (press or interference) |
👉 Best choice: 3/32″ OD tubing — it’s stock size and should slide into 1/8″ tube with minimal looseness.
✅ Pieces That Will Fit Outside 1/8″ Brass Tube
Look for tube with an inner diameter just slightly above 0.125″:
| Candidate Tube Size | Approx ID | Fit |
| 1/8″ tubing as sleeve | ~0.097″ ID | Too small — won’t fit over 1/8″ OD |
| 5/32″ brass tube | ~0.156″ OD | With ID ~0.140″–0.145″ |
| 3/16″ brass tube | ~0.187″ OD | With ID ~0.173″–0.177″ |
👉 Best choice: 5/32″ brass tube — its ID is typically just large enough to slide over 1/8″ tube with room for solder or adhesive.
🔧 Fit Types Explained
- Slip fit: slides together with slight clearance (easy assembly)
- Press fit / interference fit: very tight, may require gentle force (e.g., friction fit)
- Loose fit: gaps may need solder, adhesive, or sleeve
Based on typical brass tolerances:
- Inside fit: 3/32″ OD into 1/8″ tube → slip/close fit
- Outside fit: 5/32″ ID over 1/8″ tube → slip fit
🛠 Practical Tips
- If you need a very snug friction fit, choose a tube with an OD very close to the ID you measured on your specific 1/8″ tube.
- Brass tolerances vary; measure your actual parts with calipers before buying more.
- For a tighter assembly, ream or sand the inside tube slightly.