I assume you have checked that the 251 is the right form-factor. If so, then it is likely to be the 471 series (time lag) or the 473 series (slo-blo). Usually, the T indicates a time lag, but if Lyndel says it is slo-blo then I would be inclined to go with him.
You can see pictures of littelfuse fuses at their website (www.littelfuse.com
), which should help. You could then match the serial number at Radionics, because I can see how shipping just a fuse from the US may seem excessive.