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When you think of all the things that go into making bicycle, a couple of bolt holes on the frame, sometimes called ‘bosses’, ‘eyelets’ and ‘braze-ons’, are probably not high on the list. However, without them, you may find yourself in difficulty when it comes to adding some practical accessories to your bike. As Eben Weiss  notes in The Enlightened Cyclist:

Where you’re commuting, two things are likely: you’re going to encounter crappy weather; and you’re going to need to carry stuff. It would follow then that the urban commuting bike would include provisions for things like fenders and racks. Naturally, then, the current iteration of the urban commuting bike often takes neither of these things into account, in as much as it is modeled on a racing bike.

When buying a bicycle, it’s useful to think about how some frames  are designed to work (or not work!) with different fittings and accessories. Rather than being shrouded in mystery, here are some of the most common frame fittings to look out for.

Bottle cage bosses

Bottle cage bosses are fairly self evident. Most frames have at least two sets of bosses. Some touring bikes have a third set underneath the downtube for an extra water bottle. Bottle cage bosses are also used for attaching pumps, storage containers, and some locks.

Front fork and rear dropout eyelets

Eyelets provide attachment points for mudguards, racks, and some baskets. They are located near the front and rear dropouts. To attach mudguards and racks, it’s best to have duel eyelets (front and back) so you can fit both.

Rack mounts

Rack mounts are designed to fit luggage racks. Rear rack mounts are located near the seatstay bridge while front rack mounts are positioned mid way on the fork. Most non-racing bicycles should come with rear rack mounts, while front rack mounts are more common on touring bikes so you can carry an extra set of pannier bags.

The fork-crown and seatstay bridge (drilled)

A drilled fork-crown and seatstay bridge is common on most bicycles. The crown fork is used for attaching mudguards and front lights for dynamo systems. The seatstay bridge is necessary for attaching rear mudguards and can be used to mount a wheel lock. Make sure the fork-crown and seatstay bridge is drilled for fittings!

Chainstay bridge and kickstand plate

The chainstay bridge is the last of several attachment points for full length mudguards. Some chainstay bridges are designed to be used with a kickstand. The kickstand plate provides a more stable platform to keep your bike upright (especially when fitting a duel legged kickstands!). A kickstand plate is particularly useful on bikes that are used for shopping and carrying children.

Pump peg

The pump peg is a traditional braze-on for holding a frame pump. Since the advent of mini hand-pumps and C02 cartridges, pump pegs have become less common although they are still prized by riders who prefer the utility of a long-arm frame pump.

Tyre clearance

Tyre clearance is not a point of attachment per se, but an important frame feature. Clearance is the amount of air space between the tyre and the frame. It determines what size tyres you can fit and whether or not you can fit mudguards. Many bicycles manufactured today have a low tyre clearance because they are modeled in the style of racing bikes (see image above). However, having a wider tyre clearance is more practical because it means you more options to modify your bike as your needs change.

(Image credits: Aaron Kuehn;  ParkTools)