Summary: We discuss the structure of general anisotropic compactification in type I \(D=4, N=1\) string theory. It is emphasized that, in this context, a possible interpretation of \(M_{\text{Planck}}\) as “dual” to (at least) one of the Kaluza-Klein or windings modes could provide interesting interpretations of the “physical scales” and the GUT coupling. Some of the scenarios presented here are strictly connected with the phenomenological proposal of TeV-scale gravity (i.e. millimeter compactification). We show that in this scenario new and probably dominant effects should arise from the presence of “low-energy” winding modes of usual SM particles. Stringent bounds on the Planck mass in \(4+n\) dimensions are derived from the existing experimental limits on massive replicas of SM gauge bosons. Non-observation of winding modes at the planned accelerators could provide stronger bounds on the \(4+n\)-dimensional Planck mass than those from graviton emission into the bulk. Some comments on other possible phenomenological interesting scenarios are addressed.