MechanicalRebuild shelfHand tools, works as-is

Linear shaft

Also called smooth rod, guide rod, printer rod.

The ground steel rod a printer carriage or a scanner head rides on. Straighter and smoother than hardware-store rod. Diameters are often 6, 8, 10, or 12 mm, and 'often' is not a measurement.

If you are new to this category

Rods, gears, belts, magnets, screws, and boxes. Printers are the best source of straight steel rod and toothed belts. Screws from a laptop are tiny and specific; a random screw in a laptop hole strips the plastic. Bag them by the machine they came from.

If two parts were meshing or riding together, keep them as a pair. A gear from one toy rarely fits a gear from another.

Inside a hard drive

The two curved blocks on the steel plates are the magnets, and they are the prize. Slide them apart. Do not pry straight up. The flat coil on the arm is a short-travel motor. The platters are not a useful material, and on some drives they are glass.

Sheet metal and glass. Case steel, shattered platters, lamp glass, and magnet chips cut deeper than they look.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Size	Measure. A bushing for 8 mm will not ride 5/16 in, even if it almost does.
Hardness	Hard enough that a setscrew from a cheap pulley will not bite. Use a clamp or a flat.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

A linear slide with a bushing or a bearing
An axle
A straight edge

Leave this one when

It is bent or rust-pitted. You cannot straighten a hardened rod by eye and then expect a carriage to glide.

Buying a new one is the better idea when

Matched shaft and bearings, when the slide has to be smooth for more than a prototype.

How to tell if this one still works

Roll it on a flat surface. A bend shows up as a gap that travels.

Tools you will want: Calipers, A known-flat surface.

Where people actually find it

3 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Inkjet printer	Prize	1–2	always	The carriage rods.
Flatbed scanner	Worth it	1–2	usually	Under the glass.
Laser printer	Bonus	several	usually	Rollers.

Prize — take this firstInkjet printer1–2 · always
In this particular machine
Ground steel, commonly 8–12 mm. Measure.
Where to look
The carriage rods.
How to get it out
Slide out after the clips. Wipe the ink.
The condition to expect
Usually still straight.
Worth pullingFlatbed scanner1–2 · usually
In this particular machine
Guide rod.
Where to look
Under the glass.
How to get it out
Slide out.
The condition to expect
Good.
Bonus, if you are already in thereLaser printerseveral · usually
In this particular machine
Steel shafts, some with rubber rollers that have gone shiny.
Where to look
Rollers.
How to get it out
The rubber is often the worn part. The shaft is fine.
The condition to expect
Rubber often glazed.