Lapels - For a dinner suit there are two options for your lapel, these options are shawl or peak. Shawl lapels are only seen on dinner suits and smoking jackets, as these are very formal garments. A peak lapel is also very formal and so is perfectly acceptable on dinner suits. Regardless of which of these lapels you chose, it should always be in satin.
Pockets - A dinner suit should always have jetted/besom pockets in satin to match the lapels. Flap pockets and patch pockets both create unwanted bulk and as a dinner suit is extremely formal, it requires as little detail as possible.
Buttons - Dinner suits are traditionally single breasted with only one button. This button should always be kept fastened. The addition of a second button (which should never be fastened) creates extra unnecessary detail which is to be avoided – if it’s single breasted, it should only ever have one button. This button (and the cuff buttons) should be satin covered to match the lapels, again helping blend it into the suit and remove any unnecessary detail.
Some dinner suits in the modern age are double breasted. If the rest of the Dinner suit rules are followed, this would be perfectly acceptable at a black-tie event. However, if you are following the theme here, the less buttons on the garment, the cleaner the look is. By that rule, a 2x2 double-breasted garment will be smarter to look at than a 3x2 double-breasted.
Vents - On a British lounge suit you will likely find two vents on the back of the jacket. These allow for movement and comfort when the suit is worn all day. Dinner suits on the other hand do not need this added movement; their sole function is to make you look immaculate. It is for this reason that a true dinner suit should have no vents. No vents mean the jacket will remain stiff with little movement, reducing the risk of creasing and, as it is worn only one or two evenings a year, comfort should be of little concern!
Pants - The pants can be pleated or flat fronted, depending on taste, but must always have a plain hem (to reduce detail) and a satin band running down the outer seam to match the lapels and pockets. Some choose to have high waisted pants to prevent the white triangle of shirt showing between jacket and trouser – with the triangle gone there is no need to wear a cummerbund or waistcoat.
Waistcoat - Not seen very often these days, is a waistcoat with a dinner suit. It used to be that a dinner suit should only ever be worn with a waistcoat or a cummerbund, to stop the little white triangle of shirt from showing between the jacket and trouser. However, if you do opt for a waistcoat, it should be a horseshoe. Either double or single breasted is acceptable.
Shirt - Perhaps the biggest faux pas seen with black tie is not the suit itself – but rather the shirt that it is paired with. A dinner suit should only ever be worn with a turn-down collar, be it a kent or a cut-away. NEVER a wing-tip collar. Wingtips are to be reserved for morning wear and white tie functions. The cuff should always be a double cuff, or – again because of Bond – a cocktail cuff. Both cuffs require folding back, but a double cuff creates the need for cufflinks while the cocktail cuff fastens with buttons.
Traditionally shirts would be worn with a pleated bib, though nowadays this is seen as a very old-school style. A Marcella bib is a more modern alternative. The shirt should either have its buttons hidden under the front placket, or it should be fastened using black or pearl shirt studs.
Cufflinks & Shirt Studs - Another common faux pas is to wear any old cufflinks with a dinner suit. Cufflinks should be either in black or pearl – much like dress studs.
Pocket Square - When wearing with a dinner suit, one should only ever wear white and (if following the rule book) linen – folded into a neat rectangle. Anything more flamboyant detracts from the rest of the tidy/ immaculate look of the suit.
Bow Tie – As long as the bow tie is black, you are safe. Tiny or huge bow ties are a huge no-no. The bow tie can have pointed ends (suits a pointy peak lapel beautifully) or flat (best with shawl lapels). The edges of the bowtie should be in line with your pupils. A ready-tied bow tie is acceptable, but a self-tie bow tie is preferred.
Watch - Wearing a watch to a dinner event is traditionally unacceptable. It signifies that you are watching the time, a very rude thing to do when you have been invited to a party.
Shoes - There are only two shoes styles you can chose from, the first is a patent whole-cut oxford. The whole-cut eliminates detail on the shoe (such as toecaps) and the high shine that a patent shoe offers adds formality that your day-to-day oxfords do not have.
The second, riskier option, is to wear a formal pump with a ribbon atop the shoe. This style shoe should still be black patent leather but exposes more foot and adds a detail that some might frown upon – so wear with caution.
Socks - Traditionally. socks would always have been black silk but, - currently - if they are black, they will be perfectly acceptable.