MTB Suspension Forks

No. There are loads of different types of suspension forks depending on what type of riding you are in to and your MTB frame geometry specs. (Always use the correct length of travel fork as recommended by the frame manufacturer - longer or shorter travel can affect handling.)

Most forks have a tapered steerer from 1/8 to 1.5", some older forks are straight 1 1/8". Most forks are thru-axle with a 15mm axle interface for the front wheel, older forks were 9mm quick release. Travel is usually between 100 - 160mm depending on the type of riding they are aimed towards - shorter travel for cross country / general riding, through to long travel forks for all-mountain / downhill riding.

Wheel size is either 27.5 or 29er (older forks were 26"). There are also 27.5 Boost forks which are wider for fatter tyres and feature a longer axle  (15mm  X 110mm).

On a basic level, forks consist of a spring and a damper, most forks are air sprung, the spring rate is controlled by air pressure. The damper counters and assists the spring, controlling how fast the spring returns and how easily it compresses.

Most manufacturers recommend between  20 and 30% sag. To measure suspension sag, use a zip tie on the stanchion and  measure the difference between when you're seated on the bike (suspension compressed) and off the bike. So for example if the sag is 30mm on a 100mm fork the sag would be 30%. Use a shock pump to adjust air pressure.

This really depends on what type of riding you are planning on doing. For most cross country / general mountain bike riders, somewhere between 100 – 120mm suspension is fine for the majority of riding.If you are hitting jumps hard and taking on more challenging terrain,140mm plus will help smooth things out.