Calves: 16 ga x 1" for Resflor, Excede, Nuflor, etc. IM and to IV drugs, 3/4" for SQ
18 ga x 3/4" for SQ vaccines, 18 ga x 1" for IM vaccines
Cows: 14 ga x 1 1/2" to IV drugs in the jugular, 18 ga x 1 1/2" to IV drugs in the tail vein
14 ga or 16 ga x 1" to IM drugs or...