Left: the predicted F-mode instability strips (solid lines) for the three labelled metallicities over-imposed to the evolutionary tracks from Bono et al. (2020). Right: the same but compared with the extrapolated RRL instability strip, as predicted by Marconi et al. (2015) and shown in Bono et al. (2020) (green lines), for each selected metallicity, together with the recently derived BL Her instability strip by Deka et al. (2024) (blue lines) and the previously computed boundaries by Di Criscienzo et al. (2007) (orange lines).