Buying a new Fork

In this post we will discuss the specs and features of most aftermarket BMX Forks. 

The Offset of the Fork is the distance from the center of the fork leg to the beginning of the axle slot in the drop out. This effects stability, steering, & front wheel tricks noticeably. 
The shorter the offset, the easier it will be to initiate front wheel tricks like nose manuals or footjams. You will also notice your steering is more responsive with shorter offset forks.
The longer the offset, the easier it will be to balance front wheel tricks & the more stable your front end will feel.
Here’s a list of general recommendations for different types of riding, though it truly comes down to personal preference. 
Flatland / Streetland : 0mm – 15mm
Street / Park : 15mm – 32mm
Trails / High Air : 25mm – 35mm

The Fork Height is the vertical distance between the Wheel Base & the top of the Fork Crown. This is a pretty general spec that can noticeably change the feel of your bike.
Majority of aftermarket BMX forks are 315mm in height, which is the industry standard. However, some companies, such as S&M and WTP offer 320mm & 310mm forks.
The taller you go, the more mellow your Head Tube will feel, and your Bottom Bracket may even feel slightly taller.
The shorter you go, the steeper your Head Tube will feel, and the lower your Bottom Bracket may feel. 
Fork Height is irrelevant to Offset or Tire Clearance.

Steerer Tube Length
This is the length of the Steerer Tube, or the tube that goes into the Frame & Stem of the bike. This is another general spec to take into consideration, depending on your frame and personal preference. 
This mainly effects how high you can run your stem, & also what frame(s) the forks are compatible with.
The industry standard for Steerer Tube Length is around 160-166mm. This is ideal for frames with an average Head Tube Height.
S&M and other companies are now offering XL Steerer Tubes, which are around 170-175mm in height. These are necessary for some frames with extra tall Head Tubes. They also make a nice option for those looking to raise their stem on their bike. 

Compression Bolt
This is the bolt that holds down the stem on the steerer tube. Most high quality forks come with H24 or H25 bolts and an internally threaded steerer tube. I would avoid any forks with a welded/star nut, as they can be more likely to fail. 
Note that H25 forks have a reputation for breaking inside the stem due to the steerer tube having to be so thin. H24 is the way to go.

Heat Treatment
A lot of aftermarket forks are Heat Treated, which means the tubes have been heated and cooled in a way that strengthens them. 
The first and cheaper method is to use heat treated tubes to build the forks. However, the heat of welding can negate the treatment of the tube near the weld, which brings me to method #2..
Post-weld Heat Treatment is a process that consists of heat treating the forks post-production so that the properties of the metal are the same through out the welds. This is the most efficient way to strengthen both the tubes and the welds. 

Investment Cast Drop Outs
Investment Cast Drop Outs are drop outs that have been made in a cast with sections of the Fork legs. This makes for a bigger & more efficiently placed weld.

Integrated Bearing Race
Most high end Forks will come with an Integrated Bearing Race built into the crown/steerer tube junction. The integrated race is just a small lip that eliminates the need for a cheap, removable race.


With all of this information taken into consideration, you should be ready to pick out your own new BMX Forks! 

Info Taken from: https://www.vitalbmx.com/forums/General-BMX-Talk,2/BMX-Fork-Buying-Guide,1317982