045 O-Ring Buna-N 90A 4in ID 4-1/8in OD 1/16in Width Pack of 100

In this review the 045 O-Ring in black Buna-nitrile is evaluated for technicians, hobbyists, and anyone who needs a batch of tough, standard-size seals. The bottom line: buy this pack if you need consistent, industrial-spec O-rings that meet Aerospace Standard AS568A and resist petroleum-based fluids. The reviewer found the 90A durometer results in a noticeably stiff ring that holds shape and seals reliably, making it especially useful where durability and chemical compatibility with oils and hydrocarbons are required.

Key Features

• Material: Buna-nitrile construction provides broad compatibility with petroleum, HFCs, vegetable oils and alcohols for common sealing tasks.
• Hardness: 90A durometer gives a firm, abrasion-resistant seal that resists extrusion in moderate-pressure couplings.
• Size accuracy: AS568A Aerospace sizing ensures these rings match standard 045 grooves and fittings for predictable fit.
• Temperature range: Usable from -40 degrees F to 212 degrees F so it performs in cold storage and typical engine or hydraulic environments.
• Cross-section: Round profile creates a reliable seal between overlapping cylindrical surfaces and quick disconnects.
• Pack quantity: Supplied as a bulk pack of 100, making it convenient for maintenance shops, fleets, or repetitive DIY projects.

Who It's For

This O-ring pack is aimed at maintenance professionals, small repair shops, and DIYers who work with garden hose quick disconnects, hydraulic couplers, or marine fittings and need dozens of identical, tough seals. The firm 90A hardness and Buna-N compatibility make it a practical choice where petroleum resistance and abrasion strength matter.

Those who need extreme flexibility at very low temperatures, high resistance to ketones or ozone, or softer seals for delicate instrumentation should look elsewhere, since Buna-nitrile is vulnerable to acetone, ethers, esters and ozone and the 90A hardness is relatively stiff compared with softer elastomers.

Pros & Cons

Pros

• Meets AS568A sizing so rings fit standard 045 grooves without trimming.
• Buna-N compound balances oil and fuel compatibility with abrasion and tear resistance.
• Bulk pack of 100 delivers good value for routine maintenance and multi-unit repairs.
• Wide usable temperature range covers most workshop and outdoor applications.

Cons

• 90A hardness feels stiff to some users and can be rigid like hard plastic in hand.
• Not compatible with acetone, ethers, esters, ozone or prolonged sunlight exposure, limiting some chemical applications.

Specifications

Material	Buna-nitrile (Buna-N)
Durometer	90A
Inner Diameter (ID)	4 in
Outer Diameter (OD)	4-1/8 in
Cross-section Width	1/16 in
Color	Black
Standards	Meets Aerospace Standard AS568A

Our Verdict

The 045 O-Ring in Buna-N 90A is a solid, cost-effective choice for anyone needing many consistent, oil-resistant seals. Its firm hardness and AS568A sizing mean reliable fit and long service in common hydraulic, plumbing and outdoor equipment, making it good value for workshops and fleet maintenance where chemical exposure stays within Buna-N limits.

Frequently Asked Questions

Will these O-rings fit standard 045 grooves?
Yes. They are manufactured to AS568A sizing for the 045 O-ring, so they are intended to fit standard 045 grooves and fittings.

Are these O-rings suitable for fuel and oil?
Yes. Buna-nitrile is compatible with petroleum, HFCs and many hydrocarbons, making these O-rings suitable for fuel- and oil-exposed applications.

Do they stay flexible in cold weather?
They are usable down to -40 degrees F, but the 90A hardness makes them relatively stiff compared with softer compounds at low temperatures.