They look like a standard MR16 GX5.3 spot light fittings although depending on their actual size they could be MR11 with a GU4 base.

I wouldn't recommend fitting a Halogen bulb as they are pressurized with halogen gas, reach very high temperatures and are actually quite prone to contamination from grease and finger prints reducing the bulbs life. If you are looking for a replacement you could get LED ones which are alot safer, last longer and run alot cooler.