Outside of selecting a fork that properly fits your application, the most critical area in determining what fork is right for your machine is its lifting capacity.
Blade – The horizontal, lifting portion of a forklift fork. Measured from the inside face of the shank to the tip of the blade.
Breakout Force – Force in pounds that a machine has to “pry” material. Most commonly referred to in construction equipment like wheel loaders, backhoes, and skid steers.
Capacity – this is the maximum lifting capacity of a machine or a set of pallet forks.
Clips – Mounting brackets that are commonly welded to the back of a fork in rail-type mounting applications. Most frequently found in ITA style forklifts.
Eye – Also referred to as pin type, shaft mount or bushing type forks. This fork has a bushing, or eye welded to the shank and is typically mounted on a round shaft or bar. Most frequently found in forklifts over 15,000 lb. capacity or in telehandler style extended boom forklifts.
Heel – The bottom of a fork that contacts the ground at the 90° bend of the fork.
Safety Factor – ANSI B56 and ITSDF standards dictate that all lifting forks have a 3:1 safety ratio. This means that on a static (non-moving) load lifting forks must be able to hold 3 times their rated capacity. This provides adequate safety margins for dynamic (moving) loads to protect against permanent deflection and/or catastrophic failure.
Load Center – All loads have a horizontal and vertical center of gravity. For purposes of capacity, horizontal center of gravity is most commonly used. Load centers are calculated by dividing the actual load length in half. This gives you the horizontal center of any given load.
Shank – The vertical, mounting portion of a forklift fork. Measured from the top of the vertical portion of the fork down to the bottom of the fork, where ground contact is made.
Taper – The rate at which the blade diminishes from its original thickness to the tip of the fork. Typically a standard (approx. 1/3 of the blade) or full in which the taper starts at the heel and continues to the tip.
Nuts and Bolts Information:
Lifting forks must ALWAYS meet or exceed the capability/capacity of the machine that will use them. This is a vital lifting safety precaution, NEVER use forks that cannot pick up what the machine is rated to carry. Doing so can cause the forks to fail and can damage your load, your machine, or worse, people. Additionally, it should be noted that you should also take care not to overload your machine beyond its stated capacity and/or breakout force capabilities.
Finding fork capacity and calculating capacity load centers are simple, yet fundamental to intelligently selecting the right fork for your application. The shank, or vertical portion of a fork is stamped on the side with a (typically) metric capacity that indicates the capacity weight (kg) by the load center (mm). These two numbers provide the fork capacity rating, per fork, and the load center on which that rating is based. Fig. 1. 850 kg x 600mm
Figure 1 - 850kg x 600mm
The fork shown in Fig. 1 is rated for 850 kg at a 600 mm load center or l.c. Converting to pounds, multiply 850 x 2.24 and you have 1,904 pounds. Converting to inches, multiply 600 x .039 and you have 23.4” inches or more commonly, a 24” l.c. As a pair, these forks have a capacity of 3800 pounds on a 24” l.c.
Note: Forks without a capacity and load center stamp are highly suspect and should be avoided. Understandably, they are likely offered at a bargain price, but without a clearly stated capacity they are dangerous and are more likely to fail prematurely.
What to Watch:
The standard pallet in the U.S. is 48” long, giving a common length to compute a standard load center, 24”. Some manufacturers may use a different load center, typically 500 mm, giving the impression of a higher load capacity. To determine actual standardized capacity on a fork with a different l.c. stamp, or to calculate realistic load centers for loads longer than 48”, is simple when using the following formula:
Known capacity x known load center
New load center
3800 lbs(capacity/pair) x 24” (l.c.) / 20”(new load center) = 4560 lbs
5000 lbs (machine capacity) x 24” / 30” (new load center) = 4000 lbs
So by employing a different load center, whether shortening or extending, the capacity can change based on the length of your load or how the fork has its load center identified. While other factors can go into lifting capacity, this formula provides a simple way to approximate your lifting capabilities in most common material handling situations.