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Grey mini tower case with perforated front panel and full transparent side window

Cooler Master

Cooler Master MasterBox Q300L Grey Mini Tower PC Case

SKU CH-BPPH-VER3A

A mini-tower chassis for Micro-ATX builds with a magnetic dust-filter front, repositionable I/O panel, vertical or horizontal orientation.

  • Product typeMicro-ATX
  • Product colorGrey
  • Patterned magnetic dust filters give a distinctive look
  • Modular I/O panel moves to six positions on either side
  • Case works vertically or horizontally for flexible placement
  • Edge-to-edge transparent side panel shows the full build
  • 28 mm behind the motherboard tray eases cable routing

Grey Micro-ATX Mini Tower

The Cooler Master MasterBox Q300L is a grey Mini Tower chassis built for Micro-ATX motherboards. Its perforated front, top and bottom panels promote airflow for compact gaming or workstation builds. The edge-to-edge transparent side panel displays internal components. The case can stand vertically or lie horizontally to fit different desk layouts.

Modular I/O panel in six positions

The I/O panel mounts on either side of the chassis at the front, top or bottom, giving six possible locations. This lets builders route cables toward the most convenient edge regardless of orientation. No other case in this range offers that degree of port placement freedom.

28 mm rear routing and magnetic dust filters

Behind the motherboard tray there is 28 mm of space for clean cable runs. Patterned magnetic dust filters on the front, top and bottom snap off for quick cleaning without tools. The filters and routing depth together reduce clutter and maintain airflow over time.

How it compares

Measured against everything we stock in Tower & Desktop PC Cases, at today’s prices. Recalculated every night.

Price $35.99
Cheaper than about 93% of the 1,468 comparable items (median $100.99).

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Specifications

Product
Brand nameCooler Master
Part numberMasterBox Q300L
Product typeMicro-ATX
Product colorGrey

Questions about this item

How much space does the 28 mm cable-routing area behind the motherboard tray actually give me for wires?

It provides a dedicated 28 mm deep channel behind the tray so power and data cables can be tucked away cleanly without bulging the side panel.

What does the modular I/O panel support and where can I place it?

The I/O panel can be moved to six positions — front, top or bottom on either side — so ports stay reachable whether the case stands upright or lies flat.

Will a 360 mm long graphics card and a 159 mm tall CPU cooler both fit at the same time?

Yes, the chassis allows graphics cards up to 360 mm in length and CPU coolers up to 159 mm in height simultaneously.

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