Sentence:  Captain went out in the cab all the morning. Harry came in after school to feed me and give me water. In the afternoon I was put into the cab. Jerry took as much pains to see if the collar and bridle fitted comfortably as if he had been John Manly over again. When the crupper was let out a hole or two it all fitted well. There was no check-rein, no curb, nothing but a plain ring <WSD>snaffle</WSD>. What a blessing that was! 
Meaning of the word marked with <WSD> tags:  A broad-mouthed, loose-ringed bit "(metal in a horse's mouth)". It brings pressure to bear on the tongue and bars and corners of the mouth. Often used as a training bit.