Help customers choose the correct VoltPassThru Auto firewall pass-through by matching their cable’s actual outside diameter, required mounting-hole size, and available thread reach. AWG is a useful starting point, but finished cable diameter varies between manufacturers.
↓ Metal Size Chart (1/0 – 14 AWG)
↓ Nylon Size Chart (1/0 – 14 AWG)
↓ Sizing FAQs
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Cable O.D. Range
Measure Finished Cable Diameter
Each gland features an adjustable compression seal with both a minimum and maximum compatible cable diameter. Finished outside diameter can vary significantly between cable manufacturers, even for the same nominal AWG size. Measure the finished outside diameter of your actual cable (including jacket and insulation) with calipers before ordering.
Correct cable O.D. is important for both mechanical grip and sealing. A cable that is too small or too large for the gland’s verified range may prevent the compression seal from forming as intended. For a dust-tight, air-tight, and weather-tight cable entry, select a gland whose verified cable O.D. range includes the finished cable or cable-and-sleeving assembly.
Mounting Hole Size
Required Panel Opening
This is the required panel, firewall, or bulkhead opening for the selected gland. Openings are calibrated to allow the threaded barrel to pass through vehicle sheet metal or enclosure walls without excess play, ensuring a secure, rattle-free mounting fit.
Usable Thread Reach
Available Thread Through Panel
This describes the available threaded barrel through the mounting panel. The locknut (~3/16″ / 5mm) and two external NBR panel sealing washers consume thread depth during assembly. Refer to the usable thread reach column to verify adequate grip through double-walled firewalls, sheet metal, and panels with sound-deadening material.
Car Audio Firewall Grommet Size Chart – Metal
Constructed with a nickel-plated brass body, internal polyamide (PA) compression claw, internal NBR sealing components, and an extended threaded mounting barrel. Includes two external NBR panel sealing washers and a brass locknut for vehicle firewalls and metal enclosures.
| Nominal AWG | Model / SKU | 1 Cable O.D. Range | 2 Mounting Hole Size | Thread Barrel Length | 3 Usable Thread Reach | Loom & Fit Notes | Action |
|---|---|---|---|---|---|---|---|
| 1/0 & 2/0 AWG 0 & 00 Gauge |
GRO30001-x1 | 3/8″ – 11/16″ (10–18mm) |
Confirm against hardware (unmeasured clearance) |
11/16″ (18mm) | Ensure full nut engagement (18mm barrel) |
Catalog notes 1/2″ wire loom compatibility; verify finished OD over loom is within 11/16″ (18mm). Fits 2/0 AWG welding cable when finished OD is within 11/16″. | View 1/0 AWG Metal |
| 2 & 4 AWG 2 & 4 Gauge |
GRO30004-x1 | 1/4″ – 1/2″ (6–12mm) |
Confirm against hardware (unmeasured clearance) |
11/16″ (18mm) | Ensure full nut engagement (18mm barrel) |
Catalog notes 1/4″ to 3/8″ wire loom compatibility; verify finished OD over loom is within 1/2″ (12mm). Accommodates 4 AWG power wire within OD range. | View 4 AWG Metal |
| 6–8 AWG 6 & 8 Gauge |
GRO30008-x1 | 3/16″ – 3/8″ (5–10mm) |
Confirm against hardware (unmeasured clearance) |
19/32″ (15mm) | Ensure full nut engagement (15mm barrel) |
Catalog notes 1/4″ wire loom compatibility; verify finished OD over loom is within 3/8″ (10mm). Standard for compact amplifiers and active subwoofers. | View 6–8 AWG Metal |
| 10–14 AWG 10, 12, 14 Gauge |
GRO30010-x1 | 1/8″ – 1/4″ (3–6.5mm) |
Confirm against hardware (unmeasured clearance) |
19/32″ (15mm) | Ensure full nut engagement (15mm barrel) |
Sized for 10, 12, and 14 Gauge automotive wire; verify finished cable or bundle O.D. is within 1/4″ (6.5mm). | View 10–14 AWG Metal |
Car Audio Firewall Grommet Size Chart – Nylon
Constructed from PA6 nylon featuring a divided internal clamping structure and EPDM internal sealing components. Sized for common automotive wire gauges across single sheet metal panels, camper partitions, and battery boxes. Includes two external NBR panel sealing washers and a nylon locknut.
| Nominal AWG | Model / SKU | 1 Cable O.D. Range | 2 Mounting Hole Size | Thread Depth | 3 Usable Thread Reach | Loom & Fit Notes | Action |
|---|---|---|---|---|---|---|---|
| 1/0 & 2/0 AWG 0 & 00 Gauge |
GRO10001-x1 | 7/16″ – 11/16″ (11.5–18mm) |
Confirm against hardware (unmeasured clearance) |
9/16″ (14.5mm) | Ensure full nut engagement (14.5mm barrel) |
Catalog notes 1/2″ wire loom compatibility; verify finished OD over loom is within 11/16″ (18mm). Fits 2/0 AWG welding cable when finished OD is within 11/16″. | View 1/0 AWG Nylon |
| 2 & 4 AWG 2 & 4 Gauge |
GRO10004-x1 | 5/16″ – 1/2″ (8–12mm) |
Confirm against hardware (unmeasured clearance) |
19/32″ (15mm) | Ensure full nut engagement (15mm barrel) |
Catalog notes 1/4″ to 3/8″ wire loom compatibility; verify finished OD over loom is within 1/2″ (12mm). Compact profile for van and car builds. | View 4 AWG Nylon |
| 6–8 AWG 6–8 Gauge |
GRO10008-x1 | 3/16″ – 3/8″ (5–10mm) |
Confirm against hardware (unmeasured clearance) |
9/16″ (14.5mm) | Ensure full nut engagement (14.5mm barrel) |
Catalog notes 1/4″ wire loom compatibility; verify finished OD over loom is within 3/8″ (10mm). Sized for 6 and 8 Gauge power and amplifier wiring. | View 6–8 AWG Nylon |
| 10–14 AWG 10, 12, 14 Gauge |
GRO10010-x1 | 1/8″ – 5/16″ (3–8mm) |
Confirm against hardware (unmeasured clearance) |
9/16″ (14.5mm) | Ensure full nut engagement (14.5mm barrel) |
Sized for 10, 12, and 14 Gauge automotive wire; verify finished cable or bundle O.D. is within 5/16″ (8mm). | View 10–14 AWG Nylon |
How to Verify Fit on Automotive Wire
- Measure With Calipers: Take two caliper measurements 90 degrees apart around your finished cable to check for ovality. If your cable measures 0.58 inches, select a grommet covering 1/2″ to 11/16″ (0.50″ to 0.69″).
- Measuring Over Split Loom: When using automotive split wire loom, measure the combined outside diameter with the loom fully closed around the wire. Never force oversized loom into a compressed seal.
- Check Firewall Clearance: Prior to drilling, ensure clear access behind the firewall for the locknut and tightening tool, free from heater cores, wire harnesses, and brake lines.
Frequently Asked Sizing Questions
If your finished 1/0 AWG cable measures within the verified cable O.D. range of 10–18 mm for GRO30001-x1 metal or 11.5–18 mm for GRO10001-x1 nylon), select that model. Always measure the actual finished cable before ordering because jacket thickness varies between manufacturers, and oversized competition car audio cables may exceed this range.
American Wire Gauge (AWG) measures the cross-sectional area of the copper conductor only, not the overall outer diameter. Finished outside diameter can vary significantly between cable manufacturers, even for the same nominal AWG size, due to insulation materials and jacket thickness.
Always drill panel openings to the exact required mounting hole size specified in our chart (e.g. 1-1/8″ / 29mm for 1/0 AWG, 7/8″ / 21–23mm for 2 & 4 AWG). Deburr the hole cutout before inserting the threaded bushing to avoid damaging the sealing washers.
Yes. Finished outside diameter can vary significantly between cable manufacturers, even for the same nominal AWG size, depending on insulation material, jacket wall thickness, and stranding construction.
That depends on your installation method:
• If split loom passes through and is clamped by the gland: Measure the completed cable-and-loom assembly outside diameter with the loom fully closed around the wire.
• If split loom stops before the gland and only the cable passes through: Measure the cable itself.
Do not assume compatibility based on nominal loom size alone; the overall measured diameter must fall within the gland’s verified Cable O.D. Range.
Found Your Cable Size?
Choose the VoltPassThru Auto firewall grommet that matches your measured cable outside diameter and required mounting-hole size.
Not sure which size fits? Measure your cable’s finished outside diameter and contact us with the measurement.
