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Pin Punch Sizes: Reading Diameter and Length
A pin punch is a straight steel rod with a flat tip, used to drive a pin, a rivet or a roll pin out of a hole. It is sold with two numbers, and reading them correctly is the whole skill: the first is the diameter of the tip, which must be slightly smaller than the pin, and the second is the length of the body, which decides how much reach and how much control the tool gives.
What the two numbers mean
A punch listed as 4 by 10 is 4 mm at the tip and 10 mm of working length, with a body that is larger than the tip so the rod does not bend. The tip diameter is matched to the pin, and the length is matched to the depth of the hole and the swing available for the hammer.
| Number | What it is | How it is chosen |
|---|---|---|
| First, the tip | Diameter of the working end | Slightly smaller than the pin being driven |
| Second, the length | Length of the working section | Long enough to reach, short enough not to bend |
| Body | Thicker shank behind the tip | Provides stiffness; struck with the hammer |
| Tip face | Flat, chamfered edge | Flat for pin work, cupped for rivets |
Because the tip is thinner than the shank, a pin punch concentrates force on the pin without the rod flexing. That is the difference between a pin punch and a drift, which has a taper rather than a parallel tip.
Matching the punch to the pin
The rule for pin work is that the punch tip should be a little smaller than the pin, so it seats on the pin’s face without touching the surrounding bore. A punch that is too large will jam in the hole; one that is too small will slip off the pin and deform the surrounding metal.
| Pin size | Punch tip to use | Why |
|---|---|---|
| Around 2 mm to 3 mm | 2 mm tip | Reaches small roll pins without jamming |
| Around 3 mm to 4 mm | 3 mm tip | Common automotive and machinery pins |
| Around 4 mm to 5 mm | 4 mm tip | Larger hinge and linkage pins |
| Above 5 mm | 5 mm tip and larger | Heavy pins and rivets |
A set is generally the practical purchase, because the correct tip size is rarely known until the pin is measured. Sets are usually sold by piece count and described by total weight, which is a rough guide to how much steel is in the box rather than to the sizes inside.
Length, control and the hammer
Length decides two things. A longer working section reaches deeper into a recess, and a shorter one is stiffer and transfers the hammer blow more directly. On a stubborn pin, the short punch is the better tool because it wastes less of the blow; on a pin set deep in a bore, the long punch is the only one that reaches.
The hammer matters as much as the punch. A heavy hammer with a light punch bends the rod; a light hammer tapped repeatedly is slower but far less likely to deform either the punch or the pin. For roll pins, which are spring steel and grip hard, the correct technique is a firm, square blow with a punch that exactly fits the bore.
Pin punch options in this range
Every option in this range
Tip diameters run from 2 mm to 5 mm with working lengths from 1.5 mm to 25 mm, plus six and eight piece sets. Prices are per punch or set.
| Tip by length | Typical use | Price |
|---|---|---|
| 2 mm by 3 mm | The smallest pins and roll pins | $9.57 |
| 2 mm by 6 mm | Small pins with a little more reach | $9.57 |
| 2 mm by 10 mm | Small pins in a recess | $12.84 |
| 2 mm by 13 mm | Deep small pins | $16.70 |
| 3 mm by 7 mm | General small pin work | $10.92 |
| 3 mm by 10 mm | Machinery and automotive pins | $15.41 |
| 3 mm by 16 mm | Pins set into a bore | $20.55 |
| 3 mm by 22 mm | Deep recesses | $26.97 |
| 4 mm by 1.5 mm | A very short, stiff tip | $8.99 |
| 4 mm by 7 mm | Hinge and linkage pins | $10.92 |
| 4 mm by 10 mm | General larger pin work | $19.26 |
| 4 mm by 18 mm | Pins in deep housings | $26.97 |
| 4 mm by 22 mm | The deepest 4 mm option here | $26.97 |
| 5 mm by 10 mm | Heavy pins and rivets | $19.26 |
| 5 mm by 14 mm | Heavy pins with reach | $26.97 |
| 5 mm by 25 mm | Long heavy pin work | $26.97 |
| 6 piece set | A general spread of small sizes | $26.97 |
| 8 piece set | A wider spread including larger tips | $26.97 |
Price climbs with both diameter and length, so the small short punches are the cheapest and the long heavy ones cluster at the top. The sets sit at the same level as a single long punch, which is why they are the usual starting purchase.
Driving a pin without damaging the work
- Measure the pin and the bore before choosing the punch tip.
- Choose the shortest punch that reaches, because stiffness transfers the blow better.
- Hold the punch square to the pin so the force goes straight down the bore.
- Start with light taps to break the pin loose, then drive it steadily.
- Support the workpiece from behind so the housing is not taking the hammer load.
- Inspect the tip between blows; a mushroomed end will jam in the bore.
Roll pins, rivets and the right tip
Roll pins are made of spring steel and grip their bore under tension, which makes them the pin type most likely to resist. The correct punch for a roll pin is one that fits the pin’s inner diameter and reaches the full length of the pin, because a short punch will simply drive the pin’s top edge over and make it harder to move. A pin punch with a flat face is used here; a cupped punch is for rivet heads, where the cup centres the tool on the rounded head.
Where a pin is genuinely seized, heat and penetrating oil applied before force are far more effective than a heavier hammer. Deforming the pin head with an oversized punch turns a ten minute job into a drilling job.
Maintaining punches and drifts
The tip is the part that wears, and it wears in two ways: the face mushrooms over, and the parallel section tapers from repeated blows. A mushroomed tip should be dressed back flat on a stone or replaced, because it will no longer enter the bore it is meant for. A tapered tip has lost the property that makes it a pin punch and becomes a drift, which sits off-centre and damages the surrounding metal.
Keeping punches in a holder rather than loose in a drawer prevents the tips being knocked out of alignment, and it makes the correct size quick to find. For roll pin work, where the wrong tip costs a drilled-out pin, that is worth the small effort.
Frequently Asked Questions
What do the two numbers on a pin punch mean?
The first is the tip diameter and the second is the working length. The tip is matched to the pin and the length to the depth of the hole.
How do I choose a punch for a roll pin?
Use a tip slightly smaller than the pin’s inner diameter that is long enough to reach through it, and keep the punch square to the bore.
Should a pin punch tip be smaller than the pin?
Yes, slightly. A punch that is too large jams in the bore; one that is too small slips off and deforms the surrounding metal.
What is the difference between a pin punch and a drift?
A pin punch has a parallel tip with a flat face. A drift is tapered, which makes it easier to start but prone to sitting off-centre.
How do I stop a punch bending?
Use the shortest punch that reaches, hold it square, and match the hammer to the size. A heavy hammer on a small punch bends the rod.
Choosing the right punch
Measure the pin and the bore, choose the tip first and the length second, and keep the set in a holder so the correct size is easy to find. The pin punch range covers 2 mm to 5 mm tips in lengths from 1.5 mm to 25 mm, with six and eight piece sets for general work.
