Holding a part in position while adhesive cures, and fixing things too light for the pin's strength to matter.

Beading, mouldings, glazing beads, thin panels and cabinet backs are the usual work.

In most of those the glue provides the long-term strength and the pin simply stops the part moving for a few hours.

That reframes the selection: the question is whether the pin can hold the piece still without splitting or marking it.

Where a fixing genuinely has to carry load, a pin is the wrong choice.

Understanding this is also why the finest pin that will do the job is usually the right one.

The finest that will hold the part still - a finer gauge leaves a smaller hole and splits less.

Gauge describes shank diameter, and a higher gauge number means a finer pin.

Finer pins are less visible, need less filling and are far kinder to thin sections.

Heavier gauges hold more and are worth it where the part will be handled before the adhesive cures.

Because glue is doing the real work in most of these applications, erring fine costs little.

Tools are gauge-specific, so the gauge available may be decided by the gun rather than by the job.

Use a finer pin, keep away from the ends, and pre-drill in hardwood.

Thin sections split because there is very little material around the pin rather than because of grain direction.

Ends are the worst position, and a pin close to the end of a bead will usually split it.

Blunting the point so it crushes fibre rather than wedging it apart is effective and takes a second.

In hardwood beading a pilot from a very fine drill, or a headless pin pushed rather than driven, is sometimes the only way.

Angling adjacent pins in opposite directions holds better and reduces the chance of splitting along one line.

Head size, mostly - and how they are driven.

A panel pin has a small flat head that can be punched below the surface and filled over.

A brad has a slight or rounded head and is normally gun-driven flush in one action.

A pin nail is finer again with essentially no head, and often leaves a hole small enough not to need filling.

Terminology varies between markets and trades, so the dimensions matter more than the name.

The choice usually follows the tool available and how visible the fixing will be.

Panel pins yes; gun-driven brads and pin nails often not.

A hand-driven panel pin left flush will show and will stand proud as the timber moves.

Punching a couple of millimetres below and filling is the standard finish for painted work.

Guns drive brads slightly below the surface automatically, which is one of their main advantages.

Fine pin nails leave a hole so small that on many finishes nothing needs to be done.

On clear-finished work the filler colour matters more than the pin, so a fine pin that needs no filler is preferable.

In most of these applications the glue is the fixing and the pin is the clamp.

Beading, mouldings and panels held only by pins will loosen with handling and movement.

Adhesive spreads load over the whole joint rather than at a few points.

The pin's job is to hold the part in exact position while the adhesive sets, replacing a clamp that would be impractical.

Where a part must be removable later - a glazing bead, for instance - pins alone are correct and the reduced strength is the point.

Choosing between the two comes down to whether the part will ever need to come off.

Steel for painted work; stainless or brass where the finish is clear or the timber stains.

Ordinary steel pins are fine under paint and are the cheapest option by a distance.

Oak and other tannin-rich timbers react with steel and produce black staining around the fixing, even indoors in damp conditions.

Damp or external positions rust steel pins quickly, and the stain bleeds through any finish.

Stainless and brass pins avoid both problems and are used on clear-finished and hardwood work.

Brass is soft and bends readily, so it suits pushing into pre-drilled holes rather than driving hard.