  Grids of zero-age horizontal branch (ZAHB) models are presented, along with a
suitable interpolation code, for -2.5 <= [Fe/H] <= -0.5, in steps of 0.2 dex,
assuming Y = 0.25 and 0.29, [O/Fe] = +0.4 and +0.6, and [m/Fe] = 0.4 for all of
the other alpha elements. The HB populations of 37 globular clusters (GCs) are
fitted to these ZAHBs to derive their apparent distance moduli, (m-M)_V. With
few exceptions, the best estimates of their reddenings from dust maps are
adopted. The distance moduli are constrained using the prediction that
(M_F606W-M_F814W)_0 colours of metal-poor, main-sequence stars at M_F606W >~
5.0 have very little sensitivity to [Fe/H]. Intrinsic (M_F336W-M_F606W)_0
colours of blue HB stars, which provide valuable connections between GCs with
exclusively blue HBs and other clusters of similar metallicity that also have
red HB components, limit the uncertainties of relative (m-M)_V values to within
+/- 0.03-0.04 mag. The ZAHB-based distances agree quite well with the distances
derived by Baumgardt & Vasiliev (2021, MNRAS, 505, 5957). Their implications
for GC ages are briefly discussed. Stellar rotation and mass loss appear to be
more important than helium abundance variations in explaining the
colour-magnitude diagrams of second-parameter GCs (those with anomalously very
blue HBs for their metallicities).
