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General product information only, not medical advice. Product choice and use belong to the clinician and the manufacturer’s instructions for use.
A catheter guide wire is sized by its outer diameter in inches (for example 0.035 in), not by French or gauge. In one manufacturer’s published range the diameters are 0.018, 0.035 and 0.038 in, with tip shape, tip taper and length listed as separate specifications. Always check your product’s labelling: sizes and options differ by brand and model.
Guide wire size chart
Inch values below come from the Boston Scientific ZIPwire Hydrophilic Guide Wire product page (checked 2026-10-31). The millimetre column is arithmetic (1 in = 25.4 mm), not manufacturer data.
| Diameter (in) | Millimetres (1 in = 25.4 mm) | Listed on the ZIPwire page |
|---|---|---|
| 0.018 | 0.457 | Angled and straight tips |
| 0.035 | 0.889 | Angled, straight and J-tip |
| 0.038 | 0.965 | Listed diameter |
Other specifications on the same page are separate from diameter: tip taper of 3.0, 5.0 or 8.0 cm, and tip shapes angled, straight or J-tip. The listed J-tip model is a 0.035 in wire with a 3.0 cm taper.
How to read the chart
- Diameter is the wire’s outer diameter in inches. A larger number is a thicker wire.
- Tip shape (straight, angled, J-tip) describes the distal end. It is not a size.
- Tip taper (3.0, 5.0, 8.0 cm on the ZIPwire page) is the length of the tapered end section, again separate from diameter.
- Hydrophilic names a coating type, not a diameter or tip. The ZIPwire product is described as a hydrophilic guide wire.
- Total length is its own specification and is part of the model name, so compare it against the product’s labelling before assuming two wires match.
Guide wire types
Hydrophilic guide wire
Hydrophilic describes a coated wire. The coating is a property of the product; the diameter and tip are listed independently of it.
J-tip, straight and angled guide wires
These are tip shapes offered within the same product line. A manufacturer may offer one diameter in several tip shapes, as the ZIPwire page does for 0.035 in.
What a guide wire is, in regulatory terms
Under 21 CFR 870.1330, a catheter guide wire is “a coiled wire that is designed to fit inside a percutaneous catheter for the purpose of directing the catheter through a blood vessel” (eCFR, checked 2026-10-31). FDA’s product classification database lists product code DQX, “wire, guide, catheter”, under regulation 870.1330, device class 2 (checked 2026-10-31). The same regulation separately addresses a manually operated, non-patient-contacting torque device used to manipulate non-cerebral vascular guide wires, which is exempt from 510(k) subject to the limits in 21 CFR 870.9.
Equivalence notes
Rely on the diameter printed in the product’s labelling rather than on colour, packaging or abbreviations.
- Inches to millimetres: multiply by 25.4. 0.035 in is 0.889 mm.
- Not French: French describes catheter and dilator size. See the dilator sizes guide for how dilator sizes are expressed.
- Not needle gauge: gauge is a separate scale for needles.
Common mix-ups
- Treating tip taper (cm) or total length as the wire’s diameter.
- Reading a hydrophilic coating as a size or as a tip shape.
- Comparing a wire’s inch diameter with a catheter’s French size or an introducer’s dimensions. Related kit pages: central line kit contents, extraction balloons and esophageal dilator types.
- Assuming every brand lists the same diameters. Check each manufacturer’s labelling and instructions for use. Related introducer products are listed under introducer sheaths.
FAQ
What is a 0.035 guide wire in mm?
0.035 in is 0.889 mm (0.035 x 25.4). The ZIPwire page gives the diameter in inches only.
What are the common guide wire sizes?
The Boston Scientific ZIPwire hydrophilic range lists 0.018, 0.035 and 0.038 in. Other manufacturers list other diameters; check their labelling.
What does hydrophilic mean on a guide wire?
It refers to the wire’s coating type. It is not a diameter or tip shape.
Is a guide wire the same as a dilator?
No. 21 CFR 870.1330 defines a catheter guide wire as a coiled wire that fits inside a percutaneous catheter to direct it through a blood vessel. Dilators are sized separately; see the dilator sizes guide.
What FDA class is a guide wire?
Product code DQX under 21 CFR 870.1330 is Class II.
Sources
- eCFR, 21 CFR 870.1330, Catheter guide wire (checked 2026-10-31): https://www.ecfr.gov/current/title-21/chapter-I/subchapter-H/part-870/subpart-B/section-870.1330
- FDA Product Classification, code DQX, wire, guide, catheter (checked 2026-10-31): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=DQX
- Boston Scientific, ZIPwire Hydrophilic Guide Wire product page (checked 2026-10-31): https://www.bostonscientific.com/eg/en/products/all-products/vascular-interventions/guidewires/zipwire-/p/FP00000398
