Ko-ken Z-Series: High Torque, Low Profile Ratchets with the Smoothest Back Drag
Written by Luis Montes Updated On October 26, 2024
The Ko-ken Z-series ratchets aim to solve a common challenge in today’s heavy equipment and automobile industries: more complex and compact component designs. It has forced the tool industries to redefine their products to efficiently work into crevices, tight spaces, and hard-to-reach spots.
Ratchets, in particular, have undergone several iterations to become as compact as possible without sacrificing their ability to deliver high torque within confined spaces.
With so many brands available, it’s easy to be overwhelmed by the choice between quality, compactness, efficiency, and an affordable price.
Let’s break down the bold design decisions and clever mechanisms that make the Ko-ken Z-series a ratcheting tool with the perfect balance between low profile, super low back drag, and high torque at a fraction of the price of other popular brands.
Establishing a New Standard for Mechanics
Photo source: www.koken-tool.co.jp
Ko-ken forwent the ISO (International Organization for Standardization) and DIN (German Institute of Standardization) standards to produce sockets with smaller lengths and diameters, reducing an already compact tool.
The tables below show the width and thickness of some of the Ko-ken Z-series ratchets and compare the dimensions of standard and Z-series sockets for a 3/8″ drive anvil (with a special focus on the socket length).
| Square Drive Z-series Ratchets - 72 teeth | ||
|---|---|---|
| Model | Width (mm) |
Thickness (mm) |
| 1/4"
drive 114 mm length |
20.5 | 9.5 |
| 3/8"
drive 178 mm length |
28.0 | 13.7 |
| 1/2" drive 253 mm length |
36.5 | 18.2 |
| Comparison between Z-series and standard socket dimensions | 3/8" drive | ||||||
|---|---|---|---|---|---|---|
| S (inches) | D1 (mm) | D2 (mm) | L (mm) | |||
| Z-series | Standard | Z-series | Standard | Z-series | Standard | |
| 8 | 11.5 | 12.2 | 17 | 17.6 | 20 | 27 |
| 10 | 14 | 14.7 | 17 | 17.6 | 20 | 27 |
| 11 | 15.3 | 16 | 17 | 17.6 | 21 | 27 |
| 12 | 16.5 | 17.2 | 17 | 17.4 | 21 | 27 |
| 13 | 17.8 | 18.3 | 17 | 17.6 | 21 | 30 |
| 14 | 19 | 19.5 | 17 | 17.6 | 21 | 30 |
| 15 | 20.2 | 20.8 | 18.2 | 18.9 | 21 | 30 |
| 16 | 21.3 | 22 | 19.3 | 19.9 | 21 | 30 |
| 17 | 22.5 | 23.4 | 20.5 | 21.7 | 21 | 30 |
| 18 | 23.6 | 24.7 | 21.6 | 21.7 | 22 | 33 |
| 19 | 24.8 | 26 | 22.8 | 22.7 | 22 | 33 |
| 21 | 27 | 27.2 | 25 | 22.2 | 23 | 33 |
| 22 | 28.3 | 28.5 | 26.3 | 23.5 | 23 | 33 |
A Thinking Out of the Box Gear Mechanism
Image source: www.youtube.com/@ko-keneurope4058
Reducing dimensions isn’t enough for a ratchet to be genuinely compact. It should efficiently generate torque within a shallow angle with low back drag.
A ratchet with a high back drag or backslash won’t tight loose bolts but rather keep the socket turning back and forth endlessly, as the following video shows:
Video source: www.youtube.com/@projectpinehills.
It took Ko-ken four years to develop a new 72-tooth design and fine-tune it to produce a ratchet with one of the lowest back drags in the industry and a torque 10% greater than their previous 36-tooth model.
Source: www.youtube.com/@ko-keneurope4058.
The competition either has a decent back drag or high torque, but not both, at least as balanced as the Z-series from Ko-ken.
Let’s visually analyze the internal mechanism of some competitors against the Z-series to understand its superiority better.
Source: www.youtube.com/@CatusMaximus.
Most ratchets include springs in their internal mechanism. However, the ratchet from the above image has large springs that produce a high back drag. I mean, look at the size of those springs.
As discussed in our article about heavy equipment track adjusters, compressed springs store potential energy called “restoring force.” The restoring force increases according to the spring size.
Source: www.youtube.com/@YungJosh50.
The next ratchet has one of the most complicated mechanisms we’ve seen. Its design makes it a pain to reassemble when servicing the ratchet and increases the cost of the manufacturing process.
The combination of several teeth engaging while back-dragging, pawl friction, and a W-shaped spring contributes to the ratchet’s high backlash.
Source: www.youtube.com/@CatusMaximus.
The flaw with the model above is the fixed spring position. When the bottom of the pawl reaches the spring, it does so in an awkward position, making it hard to compress it.
Think about it this way. When you press a button, you push it straight down instead of sliding your finger over it, which would be harder and awkward.
Source: www.youtube.com/@MrSubaru1387.
The balance between low back drag and high torque of the Z-series comes from the combination of the following features:
- A dual pawl system: the lower pawl pivots while the upper one “floats” on top. The system allows only one tooth to engage while back dragging (minimizing resistance) and quickly engages all teeth when torquing.
- The spring pivots to a position where the lower pawl generates the maximum compressive force on the spring by pressing it straight down, significantly reducing the effort to back drag.
- Ko-ken even tested several spring pressures to maintain their hallmark low-torque backlash.
Don’t take our word for granted yet. Check the following videos from Tool Demos and Project Farm to verify what we’ve claimed:
Every Detail Counts
Source: www.youtube.com/@AutobahnDan.
While most manufacturers have accepted movement at the joint between a socket and a ratchet as unavoidable, Ko-ken used new technologies in its production processes to minimize tolerances across flats at the drive and head sockets.
The smaller tolerances and the new Ball Holding System significantly reduce movement in the rotating and connecting directions.
Reducing the floppiness at the joint matters, especially when working in tight spaces. Ideally, the bolt should move as soon as you rotate the ratchet.
Too much tolerance will cause a slight delay, which might not seem much unless you try to tighten several bolts within shallow-degree working angles, and instead of doing 20 passes with the ratchet for each, you do 40.
The slight delay will start to add up, making things more time-consuming, and for a mechanic, time is money.
Last Thoughts
The Ko-ken Z-series perfectly balances low profile, high torque, and smooth back drag to craft one of the finest ratchets for working in tight spaces and hard-to-reach spots.
Thanks to its reliability and hard-to-beat prices, it’s understandable why the Ko-ken Z-series has gained so much popularity among mechanics.
But again, don’t just take our word for granted. Cam, an expert heavy-duty mechanic with over a decade of experience and well-established tool brand preferences, said, “If I were to do it all over (as a heavy-duty mechanic), I hate to say it, I would outfit the trucks with Ko-ken stuff.”
Watch him reviewing Ko-ken tools in the following video: