These are very interesting antique pieces. 
They are known as CHOGS. Made from Lignum Vitae, which is a very hard wood. 
They were used for tethered horses. When a horse was tethered to the back of a stall by rope, to stop the danger of the horse getting tangled in the rope when lowering and lifting its head, a chog would be placed on the rope to weigh it down and so keep the horse safe. 
Extremely tactile and rustic and wonderful as candle holders. 
Measurements: 9cm diameter x 8cm high
*Priced individually