In most cases, snakes can swallow prey that is MUCH larger than their girth, but this should not be practiced as it can result in regurgitation (which can lead into a whole new set of problems). Also, it is important to avoid overfeeding your snake as this can result in excessive growth, pinheadedness, and drastically shortened life spans. If in doubt, it is better to slightly underfeed than to overfeed.
Happy feeding