Scientific instruments often require the integration of mechanics, electronics and optics. While the use of 3D printing techniques and commodity electronics has lowered the cost of instrumentation, the design and prototyping of optical components and light paths can be challenging and expensive. In recent years, attempts have been made to make optical devices more affordable using 3D printing as a method for production of optomechanical components. In this paper we present an assembly standard for the production of 3D printed optical devices. We describe a framework for parametric design of modular mounts, present two modules built using the framework, and demonstrate the potential for generalised design of modular optical devices following the μCube standard.