The Black Lime is undoubtedly the version of the AERO FX that plays the contrast card most boldly; here, Extrema Ratio combines a very understated black handle with a particularly vibrant orange central element, giving its small fixed-blade EDC knife an instantly recognisable identity.
Beneath this contemporary design lies the original AERO FX construction: a heavily skeletonised full-tang design, developed to reduce the knife’s weight and thickness whilst retaining a particularly robust structure.

The blade is made from Nitrogen steel and features the MIL-C-13924 bluing finish characteristic of many Extrema Ratio products. Its flat grind and compact size make it a knife designed first and foremost for everyday cutting tasks.

The black Anticorodal aluminium handle retains the interchangeable component system unique to the AERO FX range. The orange ring thus becomes a striking design feature at the centre of an almost entirely black ensemble.

The carrying system is an integral part of the design; the AERO FX comes with a particularly slim Kydex sheath as well as various accessories to adapt how it is carried for everyday use.

Technical specifications of the Extrema Ratio AERO FX Nitrogen Black Orange fixed-blade knife:
Brand: Extrema Ratio
Model: AERO FX
Version: Nitrogen Black Orange
Made in: Italy
Type: EDC fixed-blade knife
Construction: skeletonised full tang
Total knife length: 19.1 cm
Blade length: 8.0 cm
Handle length: 11.1 cm
Blade thickness: 4.8 mm
Steel: Nitrogen
Blade finish: MIL-C-13924 burnishing
Grind: flat
Handle: Anticorodal aluminium
Handle colour: black
Detail: Orange
Handle components: interchangeable
Claimed weight: 92 g
Sheath: Ultra-thin Kydex
Accessories included: additional Kydex insert, paracord and double loops for horizontal carry

Tellknives review:
Extrema Ratio could easily have produced the AERO FX solely in its usual military colours. This Black Orange version clearly demonstrates that the project is targeting a different market.

The black immediately retains the brand’s identity, but the orange completely breaks with the usual austerity of its knives. On such a compact piece, this small splash of colour is enough to visually transform the whole design.

We find the result particularly well-suited to an EDC. It remains discreet enough for everyday carry whilst being instantly recognisable when taken out of its sheath.

We’re also intrigued by the AERO FX’s design due to its focus on lightness. Extrema Ratio hasn’t simply made the knife thinner: the full-tang structure is extensively hollowed out and complemented by minimalist, interchangeable handle components.

The result therefore retains that distinctive Extrema Ratio feel whilst clearly moving away from its traditional military designs.

Of the various colourways, Black Orange is probably the most contemporary and striking. For those who love Extrema Ratio but want to move away from the usual Black, Green or Desert, this is certainly one of the most interesting versions of the AERO FX.