Autolite Parts FAQ: Spark Plug Fitments, Brake Drums, and the Strut-Shock Question

I'm a parts specialist at Autolite. On the B2B side, we work on automotive stamping, dies, CNC machining, forgings, and extrusions. On the parts desk, I handle the fitment questions that show up with every rush order. I've handled more than 200 of those in the past six years, and they usually start the same way: 'I need this before Monday.' This FAQ is the conversation I keep having with buyers, counter staff, and mechanics. Skip to the question you need.

What do Autolite 45 spark plugs fit?

What do Autolite 45 spark plugs fit? The short answer: a lot of older engines, especially small-block Fords from the 1960s and '70s, some inline-six engines, and a list of marine and industrial applications. The Autolite 45 is a conventional 14mm gasket-seat plug. But the longer answer is the one that matters: the application guide is the final word, not the vehicle name.

According to Autolite's application guide (autolite.com, accessed January 2025), the 45 is listed for specific engine families, not just 'any old Ford.' If a customer says it's a 302, check the block casting. If the engine was swapped, the old chart won't help you. My rule on old plugs: the part number is a clue, not a contract.

I don't have hard data on how many 45s are still in service, but based on the orders I've handled, the number is higher than the classic catalogs suggest. My experience is mostly with North American engines; if you're working with an imported or crate motor, the same part number may not apply. The parts are still in use, but don't assume a plug that fits one 302 fits every 302.

What about Autolite spark plugs 25?

Autolite spark plugs 25 is a separate part number, not a heat-range code. It has a different reach and heat range than the 45, and it still shows up in the Autolite catalog for older engines that call for it. If you found '25' in an old tune-up spec, the catalog is where to verify the replacement.

Look, I get why people want a shortcut. 'The engine is from the '70s, just give me the plugs.' But the 25 vs. 45 question is exactly where a wrong part shows up. The number changed over the years—sometimes because of heat range, sometimes because of seat type. If you're substituting a modern plug, check the gap and the heat range before you start wrenching.

I have mixed feelings about old part numbers. On one hand, they keep classic engines running. On the other, they get treated as interchangeable when they aren't. The Autolite catalog takes two minutes to check. The engine doesn't.

What should I check before ordering a rear brake drum?

Rear brake drum failures in rush work are almost never a manufacturing defect. They're a measuring problem. Before you order, you need the inside diameter, the width of the friction surface, the bolt pattern, and the offset. You also need to know whether the vehicle has been converted to disc brakes in the rear—that changes the mounting surface, not just the drum size.

I still kick myself for the time I ordered a rear brake drum for a delivery van without checking the casting number. The invoice said it fit. The metal didn't. Two days of rush freight later, the customer was out $219 and the van was still off the road. Ten minutes with a caliper would have caught it.

And if you're working in a cold shop, one more thing: a space heater with thermostat is fine for the room, but don't use it to warm up a drum before you measure it. Heat changes the diameter. Measure the drum cold, at shop temperature, or you'll end up with a part that fits in the afternoon and locks up at 6 p.m.

When in doubt, replace drums in pairs. A new drum on the left and a worn drum on the right gives you different brake balance. That matters more on a loaded work truck than on a sedan.

What's the difference between a strut and a shock?

The difference between a strut and a shock is not just a vocabulary test. A shock absorber is a damping device. It controls the movement of the spring, but it does not support the weight of the vehicle. A strut is a structural component. It contains a shock inside, but it also holds the spring, supports the corner of the car, and often serves as the upper mounting point for steering and alignment.

Why does this matter for a parts order? Because you can replace a shock without changing the vehicle's alignment. If you replace a strut, the vehicle needs an alignment after the job. The repair order may say 'shock' because that's what the customer typed, but the car may be built with a strut. The question isn't 'shock or strut?' It's 'what suspension layout does this vehicle have?'

This is another place where the old approach—look at the part and match it—doesn't work anymore. Coil-on-strut designs, cartridge-style struts, and shock/spring assemblies all changed the rules. The fundamentals haven't changed: a shock damps, a strut supports. But the execution has transformed.

Why do you ask for a VIN or casting number on a rush order?

Because the part number on the box is only half the answer. The other half is what the vehicle actually has. The same truck with a different brake package can take a different rear brake drum. The VIN decodes those options faster than a wrench can.

I've had a customer insist on a rear brake drum because 'the computer said it fits.' The computer was right for the base model. The truck was not the base model. Now I ask for the stamped casting number before I even quote the part. It adds thirty seconds to the call and can save two days.

How do I handle an Autolite rush order without turning it into a fire drill?

Rush orders are where I've earned my gray hairs. I've processed 200+ of them, including same-day turnarounds for shops that had a customer's car on a lift. Here's what I've learned: the only thing you can really compress is shipping time. You can't compress the checking time.

In March 2024, a shop called at 5:30 on a Thursday with a rear brake drum for a shuttle van that had to be on the road by Saturday. Normal delivery was four days. We agreed on the part number, paid $119 for air freight on a $72 drum—$191 all in, actually—and delivered Friday afternoon. The alternative was the shop losing a weekend charter job. That was the real cost. Total cost beats base price every time.

What was best practice in 2020 may not apply now. More vehicle lines, more variants, and more old models being kept on the road means the parts catalog changes constantly. But one rule still stands: verify the part before you pay for the fast shipping. The most expensive order is the one that has to ship twice.