.139" Buna-N 70 Square O-Ring Cord Stock Black

Made from black Buna-N (Nitrile) at 70 durometer, this cord delivers strong resistance to oils, fuels, and everyday industrial fluids. The square profile provides added sealing surface and stability compared to standard round cord, giving you a tighter, more consistent seal in demanding applications.

Get a reliable seal exactly where you need it, without waste or guesswork. This .139" square Buna-N 70 O-Ring cord stock is built for customers who need flexibility, fast turnaround, and dependable performance. You can cut it to length, create custom O-Rings, or replace worn seals on the spot, helping reduce downtime and keep your equipment running.

Operating temperature: -30° to +212°F (-34° to +100°C)

This Buna-N cord is engineered for reliable performance across a wide range of operating conditions. It maintains flexibility in lower temperatures while holding its shape and sealing force under moderate heat and pressure.

Material & Performance Details

This square O-Ring cord is manufactured from high-quality Buna-N (Nitrile) elastomer, one of the most widely used sealing materials in the industry due to its balance of cost, performance, and durability.

Durometer: 70 Shore A
Color: Black

Performance strengths include excellent oil resistance, good abrasion resistance, and low compression set for long-term sealing reliability.

Excellent resistance to:

• Petroleum-based oils
• Diesel and gasoline fuels
• Hydraulic fluids
• Mineral oils

Limited capability with:

• Ozone exposure
• Sunlight and weathering
• Mild acids and chemicals

Not compatible with:

• Strong oxidizers
• Ketones
• Chlorinated hydrocarbons

Sizes & Measurements

• Cross Section (CS):
  • 0.139" nominal
  • Actual: 0.134" ±0.006"
  • 3.53mm nominal (3.40mm ±0.15mm)
• Inside Diameter (ID): Custom cut to your requirement
• Outside Diameter (OD): Custom based on formed length
• Part Number: SN70.139
• Sold by the foot, continuous lengths available

Applications & Use Cases

This square Buna-N cord is widely used across industries where custom sealing is needed quickly and reliably. It is ideal for maintenance teams, repair shops, and OEM applications that require flexibility in sizing.

Common uses include hydraulic systems, pneumatic equipment, pumps, valves, agricultural machinery, automotive repair, and general industrial sealing. It is especially valuable when a standard O-Ring size is not available or when immediate replacement is required to keep operations moving.

Key Specifications

• Material: Buna-N (Nitrile, NBR)
• Durometer: 70 Shore A
• Color: Black
• Temperature Range: -30°F to +212°F (-34°C to +100°C)
• Profile: Square Cord
• Length: Sold per foot, bulk spools available
• Country of Origin: USA
• Certifications: Available upon request

Why Buy from The O-Ring Store LLC

When you buy from us, you are getting more than just cord stock. You are getting a partner focused on helping you solve problems fast and correctly the first time.

We operate under ISO9001:2015 certified processes, which means consistent quality and full traceability when you need it. We stock in the USA for fast delivery, and most in-stock items ship the same day so you are not waiting on critical parts.

If your application requires something custom, we can help with cut lengths, vulcanized O-Rings, or material guidance. Our team works directly with you to make sure you get the right seal, not just a part number.