Thomson Linear Bearings and Saginaw Actuators: An Engineer's FAQ on SG90 Servos, 6806 Bearings, and Pete Jackson Gear Drives

The parts questions I actually get

I'm an applications specialist at thomson-linear, and a large part of my job is helping people fix machines before the plant shuts down. In the last nine years, I've handled maybe 200 rush orders—or closer to 180, I'd have to check—including same-day turnarounds for a hospital automation line and a steel mill. This FAQ is a sample of the questions that keep showing up in my inbox. If you're trying to source a bearing, an actuator, or a motion control part and the lead time from the original supplier is too long, start here.

Are Thomson linear bearings worth the premium over generic bearings?

Yes, in most applications I review—but not for the reason people expect. The real advantage isn't that every Thomson linear bearing is magical. It's that the tolerances, raceway geometry, and load ratings are documented, so you can verify them. Thomson linear bearings are designed to work with shafts that are ground and hardened within a specific range.

If you put a generic open bearing on a properly ground shaft, it can work fine. If the shaft is undersized or soft, the generic bearing may not last as long. I've seen 'same specification' bearings cost 40% less and run noticeably hotter. Wait, that's not exactly right—the few that failed ran hot, not all of them. The issue was the cage design. The point is, the bearing number only gets you in the right ballpark. Engineering data gets you the right part.

Can a Thomson Saginaw linear actuator replace my old acme screw system?

A Thomson Saginaw linear actuator usually refers to a ball screw or actuator assembly that converts rotary motor motion into linear motion with rolling elements instead of sliding friction. That gives you lower running friction, higher efficiency, and more consistent positioning than an acme screw. If your cycle rate is low and your load is moderate, a plain leadscrew can do the job for less money. But when you need precise positioning, long life, or higher thrust, a ball screw actuator is the stronger choice.

The catch is that you need to match the lead to the motor and the load. A high lead gives more speed and less thrust; a low lead gives more thrust and less speed. I helped a customer in March 2024 replace a Saginaw-style actuator on a labeling line—actually it was a packaging line, but same idea—36 hours before a scheduled production run. The critical dimension was the mounting flange. We verified the lead, stroke, and flange before ordering. It fit, and we shipped it overnight. Had we assumed the model number was enough, we'd have been wrong.

Is an SG90 micro servo motor okay for motion control?

For a hobby project, absolutely. For a production machine, no. An SG90 is a small 9-gram servo with plastic gears, a very low duty cycle, and no absolute encoder. It is great for a robot arm, a camera gimbal, or an engineering class. It is not a substitute for a real motion control servo or a stepper motor.

People often ask if they can use an SG90 to drive a small linear actuator. The stall torque on a common SG90 is around 1.5 kg-cm, depending on supply voltage. That's enough to move a lightweight lever, but not enough to drive a ball screw under load. If you're testing a concept, fine. If your project needs to run even a few hours per day, buy a proper motor and actuator combination.

I like that people start with SG90s. Small doesn't mean unimportant—it means potential. A customer once ordered one SG90 to test a mechanism. That test turned into a $30,000 servo system order later. We took the small order seriously, and it paid off.

What should I check before ordering a 30x42x7 ball bearing (6806)?

First, decode the number: 30 mm bore, 42 mm outside diameter, 7 mm width. That's a 6806 deep-groove ball bearing. Before you buy, check the seal type, cage material, internal clearance, and load rating.

• Seal or shield: 6806-2RS has two rubber contact seals. 6806ZZ has metal shields. An open bearing lets in debris, but it's easier to relubricate.
• Cage material: polymer cages are quiet and common; steel cages handle higher temperatures and some harsh environments.
• Internal clearance: CN is standard for most applications. C3 is common when you have a tight press fit or high temperature.
• Speed and load: a 6806 in a 10,000 rpm motor is a different part than one in a 1,500 rpm conveyor idler. Check the dynamic load rating against your actual radial load.

The quickest way to get into trouble is ordering by dimensions alone. In Q3 2024, I asked three suppliers for the same 6806-2RS and got quotes from $9 to $21. The cheap one was actually a ZZ version with metal shields, not a 2RS. It might have worked. But for a machine that can't afford downtime, I chose the one with documented specs.

And don't forget the total cost. A $9 bearing can become a $5,000 repair if it fails in an expensive gearbox. Prices change, so verify current quotes before you order.

What happened to Pete Jackson gear drives?

People still ask about Pete Jackson gear drives, even in a motion control FAQ. They were popular aftermarket timing gear drives for older V8 engines. Instead of a timing chain, they used gear-to-gear contact to spin the camshaft, which gave a distinctive whine and a strong visual appeal.

What happened? I can't give you the full corporate history. From the aftermarket listings I've seen in early 2025, the product has faded from the mainstream. Engine builders have moved to stronger, quieter timing-chain systems. The Pete Jackson name still shows up as new-old-stock and used parts, but you're mostly on your own for technical support.

The lesson for a motion control engineer? A famous nameplate is not a spec. I see the same pattern with old Thomson Saginaw parts. If you buy a legacy gear drive or actuator, inspect it, check the instructions, and verify the mounting. A cool part with the wrong bore or backlash is just a paperweight.

What if I need one bearing or actuator tomorrow?

That's the call I get almost weekly. When a machine is down, time matters more than price. The first thing I ask is: what is the exact part number? If nobody knows, I ask for dimensions, load, speed, and a photo. Then I get real about the timeline.

In Q4 2024, we processed 47 rush orders with 95% on-time delivery. One was a single 6806 bearing for a wastewater pump, shipped overnight for $65, and it saved a $12,000 maintenance window. Another was a $15,000 linear actuator for a hospital automation line. Same process, different paperwork.

Once, I had two hours to decide on a rush bearing for a production line. The line was losing more money per hour than the bearing cost. Normally I'd compare freight options, but there was no time. I paid for overnight shipping and moved on.

The value of a rush order isn't just speed; it's certainty. Knowing that your deadline will be met is often worth more than a lower price with estimated delivery. And you don't need to be a big account to get a straight answer from me. I still remember the vendors who treated my $200 orders with respect when I was an engineer with a shoestring budget. I'm not going to pass that disrespect along. If you need one part, I'll help you buy one part.