i have a d16z6 vtec that i've been reubuilding and it's the first time i've done anything with engines but i have someone overlooking what i'm doing and teaching me everything, i've come acrossed a few thread holes on the head that i'm not sure what they're for, there's 3 i believe the smaller one is for coolant temp still not 100% if someone could help me i would appreciate it thanks.

i took some pictures to help pin point what im referring to. (yes im missing a transmission bolt atm)

 

Largest opening on the Left: Port for heater core male barb.
Smallest opening in the Middle: Single wire bullet type sensor for engine coolant temperature (gauge cluster)
Medium opening on the Right: Two wire sensor for engine coolant temperature (ECU)

 

thanks for the info, i'll start the search for those once i'm off work today.