A cufflink gift almost never fails because of the cufflinks. It fails because of a shirt.
I have bought this gift three times now, and every time the thing I could not work out from a product photo was the same: what is actually in the box, and will his own pair fit if I buy the box on its own. Those two questions have real answers. Here they are, along with the tie bar length question that catches people out at weddings.
Cufflinks only work on double cuffs, sometimes called French cuffs: the long cuff with no button at the wrist, meant to fold back on itself. If every shirt he owns fastens with a button, a pair of cufflinks is a gift he cannot use this week, or possibly this year. We wrote a full walkthrough on how double cuffs work and how to put a pair on if you want to check his wardrobe before deciding.
So the first fork is simple. If he already wears double cuffs, a set is a good gift. If he does not, and you are not also buying the shirt, a box he can fill later, or a tie clip he can use with any shirt, lands better than cufflinks he has to store.
Most confusion comes from the fact that "cufflink box" describes three different purchases. What separates them is simply whether the accessories are included.
1. The box that includes a pair. Our window-lid cufflink box is solid black walnut, 47 × 47 × 30 mm, about 30 g, with a magnet at each corner and a clear acrylic window in the lid so the pair is visible before the box is opened. A pair of round cufflinks is supplied with it, in one of five finishes: gold, silver, rose gold, gunmetal or black.
Buy this when: he owns no cufflinks, or you want the gift to read as a gift the second he sees it.
2. The box on its own. The square walnut box has a fitted tray with two cufflink slots and a channel for a tie clip, so nothing rolls around. Accessories are not included. The lid takes a name, a date, or one of eleven ready-made layouts.
Buy this when: he already has pairs living loose in a drawer.
3. The complete set. Two versions, identical apart from one measurement: a pair of 18 mm brass cufflinks with either a 45 mm tie clip or a 55 mm tie bar, each piece in its own slot in an engraved walnut box.
Buy this when: you want one parcel to be the whole gift, with nothing else to order.

A fitted tray holds each piece in a shaped slot. A lined tray without slots will take almost anything, but the pieces move in transit.
This is the part product photos rarely answer, and it is the reason boxes get returned.
The face. Measure across the widest point of the decorative front. Ours are 18 mm, which is a common size for a plain round or square link. If his are statement pieces, oversized novelty links, or vintage, they may be considerably wider than that, and a slot cut for an 18 mm face will not take them.
The back. Cufflinks close in several different ways, and the closure decides how they sit in a box more than the face does. A fixed toggle, the little bar that swivels flat, is rigid and short. Chain-link cufflinks have two faces joined by a loose chain. Silk knots are soft and squash. A shaped slot is cut around a rigid toggle, so chain links and knots tend to sit proud of it rather than settle in.
There is a quick way to judge any brand's box from its photograph, ours included. Look at how the cufflinks are sitting in the picture. If each one is held in a cut recess that matches its outline, that is a fitted tray, and it will hold a pair of that size and refuse anything much bigger. If they are simply lying on a flat lined base, it will take almost any pair, but they will shift when the box moves.
If you are buying a box for a pair he already owns and they are not a standard 18 mm toggle style, message us with the measurement before you order. It takes a minute and it is a great deal easier than a return.

The two sets look the same in a photo, and the difference matters more than the price does. The convention is that a tie bar should never be wider than the tie it holds. Sitting somewhere around three quarters of the tie's width is the traditional guide, and a bar that overhangs on both sides is the one detail that photographs badly at a wedding.
So do this rather than guessing: lay the tie he actually wears flat, and measure straight across at its widest point. A full-width tie takes the 55 mm bar. A slim tie takes the 45 mm. If you are buying for a man whose ties you have never seen, the 55 mm is the safer default, because full width is still the standard cut for a business or morning tie.
One thing worth knowing if this is for a wedding party: buy all the bars the same length even though the groomsmen's ties are identical only in theory. It is the kind of small consistency that shows in the photographs. We covered the wider version of this problem in our guide to what to give each role in the wedding party.
I would rather tell you this than have you find out afterwards. The single most common reason a personalised piece comes back to us is an engraving error, and nearly every one of them traces back to wording that nobody read back to themselves before it was cut. Once the laser has run, the mark is permanent. That is the point of it.
Three practical things follow from that.

On the window-lid box the engraving is cut into the acrylic itself, so the walnut grain underneath stays unmarked.
Do that and the parcel leaves us the same day the order is placed, which is the question our customer service team is asked more than any other.
He has no double-cuff shirts. Is a cufflink gift still worth giving?
Only if you are giving the shirt too, or if you know he is heading into an occasion that calls for one. Otherwise a box with a tie clip is the better version of the same idea, since a tie clip works with any shirt he already owns.
Can I put cufflinks he already owns into one of your boxes?
Usually, yes. The fitted trays are cut around an 18 mm toggle-back pair, which covers most plain cufflinks. Oversized, chain-link or silk-knot styles are the ones to check first, so send us the measurement across the face and we will tell you before you order.
Which tie bar length should I buy for groomsmen?
Buy to match the ties. If the wedding ties are full width, order 55 mm for everyone; if they are slim, order 45 mm for everyone. Mixed lengths across one line-up is the thing you will notice in every photograph afterwards.
What should go on the lid if it is a group gift?
Each man's own name works better than the event or the date. A name makes the piece his and keeps it useful after the event, which is exactly what stops it becoming another handsome object that stays in its box.