the halo and subhalo spin distributions. We examined the influence of (sub-)halo finder, spin parametrisation and resolution to confirm that these factors are not the origin of the difference between the halo and subhalo spin distributions. In this process we confirmed the difficulties that the [<span style="font-variant:small-caps;">ahf</span>]{} finder has in recovering substructures reliably where the density contrast between the main halo and the subhalo is low. We recommend that the [<span style="font-variant:small-caps;">ahf</span>]{} halo finder should be treated with caution in situations where a complete unbiased sample of the subhalo population is required.

In this paper, we have argued that the difference between the spin distributions is physical and it is caused by tidal stripping of sub[haloes]{} removing high angular momentum material. This argument is strongly supported by three pieces of evidence presented here. Firstly, sub[haloes]{} tend to have lower spin when compared to [haloes]{}of the same mass. This discrepancy gets larger towards the low mass end. Secondly, the spin distribution of sub[haloes]{} is radially dependent within a host halo. Sub[haloes]{} closer to the host halo center, which are expected to have been more tidally stripped, have lower spin than those closer to the virial radius. Thirdly the difference between halo 