CMS-Japanese Motorcycle Supply Parts

Ko-Ken 3/8" Extension Set PK3760/6 Review


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Today I'm reviewing the Ko-ken 3/8" (or 9.5mm) extension set PK3760/6 (eBay US, eBay CA, eBay AU). If you aren't familiar with the brand, Koken are a Japanese manufacturer who specialise in socketry and related tools. This particular extension set is the non-wobble variant - the wobble variant is part number PK3763/6 (eBay US, eBay CA, eBay AU). What's the difference? The wobble-fix extensions have a cut-in that allows for 15° of movement for whatever is attached to the male end. Why wouldn't you just buy the wobble-fix? Koken say that "The Wobble-Fix Extension Bar has less strength than normal extension bar (sic) due to it's specific design with a reduced square drive."

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

The PK3760/6 set has six extensions included - 32mm, 50mm, 75mm, 150mm and 250mm. The entire range of Koken's standard 3/8" extensions is a good deal more expansive than that selection and includes 300mm, 400mm, 500mm, 600mm, 900mm and 1,000mm extensions.

As you can see it comes in an ABS case, wrapped in plastic:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

On the back is a paper insert:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

Country of origin lower left:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

Sizes on the right:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

Turns out the knurling is patented:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

With the plastic removed we can see the contents:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

The knurling feels as nice as it looks:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

The grip provided by the knurling is good and works well. It doesn't make it as easy to freely spin the extension as a quick spinner (like the Koken 3756Z) but it's miles better than a smooth chrome extension, particularly with oily fingers.

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

The corners of the female end are rounded, which is good as it means that the force will be transferred across the flats rather than the corners:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

There's a detent on the inside to receive the ball bearing to retain the extension on the ratchet wrench/other extension/etc.:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

The brand and part number - the last part of which is the length - is marked on each of the extensions:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

...along with the country of origin:

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

In use the extensions are top notch - they fit very tightly, much more so than the Taiwanese-made Kincrome set I usually use (K2924, slightly cheaper than the Koken on eBay AU). The knurling is nice under the fingers and provides good grip, with the additional benefit of preventing the extensions from rolling away. If you put a socket on it's side I think you expect it to roll somewhere - hard not to leave extensions on their side, though, and it has been a nice experience having them not roll anywhere due to the knurling being separated into six separate sections with gaps inbetween.

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.

The range of lengths in the kit is quite useful for the work I do on motorcycles and cars (largely Japanese). The slop in these is minimal, particularly when paired with a quality ratchet like the Nepros NBRC390L or the Koken 3725Z (eBay US, eBay CA, eBay AU). Speaking of Koken's Z-series, there are a couple of extensions available from it - as of the May 2019 Japanese catalogue they only have 75, 125 and 250mm lengths listed as part numbers 3760Z-75, 3760Z-125 and 3760Z-250. So, if you're set on the Zeal range you'll have a lot fewer choices extension-wise - and you miss out on the knurling!

After using them for a week I can wholeheartedly recommend them as a quality extension set - the range of lengths is useful, the knurling is a nice feature and they're not badly priced (check links above!).

Here is a review of the Koken or Ko-Ken PK3760/6 3/8-inch socket extension set - made in Japan.



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