Here is a link that shows that the "T" designation is for slow-blow fuses:
http://www.ehow.com/about_6525933_difference-between-ceramic-glass-fuses.html
Quoted from article: "The fuses available are very fast acting fuses (FF), fast-acting or quick-blow fuses (F), medium-acting or semi-delay fuses (M), slow-blow, time-lag or time-delay fuses (T) and very-slow-acting, long-time-lag or super-time-lag fuses (TT)."