  We present the GAMBIT modules SpecBit, DecayBit and PrecisionBit. Together
they provide a new framework for linking publicly available spectrum
generators, decay codes and other precision observable calculations in a
physically and statistically consistent manner. This allows users to
automatically run various combinations of existing codes as if they are a
single package. The modular design allows software packages fulfilling the same
role to be exchanged freely at runtime, with the results presented in a common
format that can be easily passed to downstream dark matter, collider and
flavour codes. These modules constitute an essential part of the broader GAMBIT
framework, a major new software package for performing global fits. In this
paper we present the observable calculations, data, and likelihood functions
implemented in the three modules, as well as the conventions and assumptions
used in interfacing them with external codes. We also present 3-BIT-HIT, a
command-line utility for computing mass spectra, couplings, decays and
precision observables in the MSSM, which shows how the three modules can be
easily used independently of GAMBIT.
