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The Parts and Accessories Encyclopedia


MK23 users have always been innovative and quick to find a solution to a problem, and when users found that their pistols were unable to effectively hop 0.30g or higher weight BB's, modifications were performed to allow the hop arm to lift heavier weights than previously used before. For example, by creating mods with rubber wire, inside of pens and pieces of card to improve the contact pressure that the hop arm applied to the hop rubber mound in order to lift heavier weight BB's.

The Top Down Center modification originated from the bolt action / sniper community where a hold would be drilled through and above the hop unit so that a screw could be directly lowered down on to the hop arm to apply direct and constant pressure on the hop rubber mound. This mod became a standard DIY upgrade for many bolt action users, before naturally being adopted in other platforms like pistols. 

With the rise of 3D printing, innovative designers have developed parts for almost every platform that allows users to easily upgrade their systems with a TDC style part. The MK23 is no exception to this innovation and since the arrival of dedicated TDC parts, the MK23 has reached entirely new levels of performance and range capabilities.

Please find below a list of the communities most recommended aftermarket Hop Nub upgrades. Hub Nubs on this list have been tried and tested in Airsoft skirmishes over several months and have proven to remain durable and reliable in use for the tested period.



| Hadron Airsoft Design TDC Cover |


The Hadron Airsoft Designs TDC Dust Cover is available from the following retailer:

HAD TDC Cover V2 - Link


"The most important mod on the MK23." - Kicking Mustang (Link)

"Hell yeah! TDC boiz!" - Brad Green

"So I got my TDC covers today. I haven't got to properly test them yet, but more important than their function my initial thoughts were. I didn't expect them to be so furry. Now I know what your thinking "wtf is this guy on about?" . Well it's quite simple I like them because they feel furry, I may even buy some more. Just to keep in my pocket and stroke. A bit like Lenny from "Of mice and men".

 - Heroshark

Can be difficult to obtain outside of the UK/EU

Lacks realism of stock dust cover

A revolution to the MK23

Utterly essential

Very effective

Hard to obtain in US/Asia




Lightweight design

Very easy install

Reliable hop pressure

External adjustment

Can lift heavyweight BB

  • Low profile, does not interfere with holsters.

  • Compatible with the Tokyo Marui MK23

  • Compatible with all clone MK23's.

  •  Does not require the use of the dust cover spring.

  • Can apply enough pressure to easily overhop 0.50g BB's.

  • Applies pressure directly to the hop arm plate.

  • Designed to be used with the Hadron Airsoft Designs H Plate.

  • Removes the need to use the standard hop wheel.

  • Provides secure and reliable fit.

  • Can be used with the stock hop rubber and barrel.

  • Compatible with aftermarket barrels and rubbers.

  • Hop pressure can be applied externally without removing the slide.

  • No tools required.

  • Easy and quick installation.


Born out of pure invention and necessity to overcome a weakness in the MK23 platform, Hadron Airsoft Designs entered the MK23 community as a overnight household name in 2016 with their now famous and for many, essential TDC cover upgrade part. Since their arrival, they have continued to provide innovation after innovation for the MK23 community and their MK23's. In this case, the now famous "TDC" dust cover replacement.

The TDC, or Top Down Center Dust cover from Hadron Airsoft Designs is a full dust cover replacement part. The TDC sits securely in the position of the stock dust cover where it provides an adjustable grub screw directly above the position of the hop arm. When the TDC screw is lowered down on to the hop arm, it applies direct and centered downward pressure on the hop arm to ensure perfect contact and spread pressure on the hop rubber mound.

This perfect contact pressure allows the rubber to transfer enough friction and backspin to the BB that weights as heavy as 0.50g can be projected up to distances of 70 meters or more with level flight. The TDC cover has replaced traditional DIY methods and modifications to the point where it is now more uncommon to see a stock MK23 than it is to see a MK23 fitted with a TDC cover; which is a true testament to it's effectiveness as an upgrade part.

The TDC is usually partnered up with either a Maple Leaf I-Key or Hadron Airsoft Designs H-Plate due to the additional results achieved by combining the two parts. Adding either of these parts requires less adjustment from the TDC.

Hadron TDC


If you know of or have used an aftermarket part that you believe should be listed here, please feel free to submit a recommendation for review.

Thanks! Message sent.

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