85% infill recommended, printed with ABS.

Close model of the one George Matheis (Modern Combatives System) designed for Alpha Innovations, only I optimized it a bit for 3D printing namely a tad thicker webs and a better palm swell for those with less meaty hands.

FWIW plastic knuckles are LEGAL in Canada (where I reside) as per this CBSA document (it is YOUR responsibility to confirm legality in your country of residence, I cannot be held responsible):

http://www.cbsa-asfc.gc.ca/publications/dm-md/d19/d19-13-2-eng.html#a4x2

46. Brass knuckles can be combined with other weapons such as knives. These ‘brass knuckles knives' consist of two parts: a knife blade, and brass knuckles integrated into the handle. The blade part does not generally possess characteristics that would make it fall under the definition of prohibited weapon. Rather, it is the brass knuckles handle that will usually determine the knife's classification as a prohibited weapon. In order for the knife to be prohibited, the brass knuckles part of the knife must meet the definition of "brass knuckles" in the regulations. Therefore, to classify a ‘brass knuckles knife' as prohibited:

(a) the handle must be a weapon; and
(b) that weapon must meet the definition of brass knuckles. It is not sufficient for the blade portion of the knife to be designed as a weapon.

Exception: The following goods generally do not meet the definition of prohibited weapon, and thus do not fall under tariff item 9898.00.00. Their misuse may nonetheless be punishable under other laws:

(a) plastic knuckles do not fall within the definition of "brass knuckle";
(b) D-guard knives (knives with a hand-guard in the form of a "D").

FOR EDUCATIONAL/NOVELTY PURPOSES ONLY, VIRTUAL RENDERING/PROOF OF CONCEPT

See proper knuckle usage here (coincidentally taught by the designer):

https://www.youtube.com/watch?v=1QKHQuGcJ0U

https://www.youtube.com/watch?v=njW0gIrp-wE

http://www.moderncombativesystemsblog.com/2016/08/knuckles-101-part-i-selection-carry.html