I have seen a sprocket used as a tensioner wheel here on the forum, the trick is finding a sprocket that works with your chain. Most industrial idler sprockets are wider and are for a #40 chain, the chain rollers and pin placement are the same. You would have to turn or grind down the teeth so the chain would fit. The #41 chain will be the easiest to get the sprocket turned down to fit.
ain Number
*Pitch
*Roller Diameter
Betwwen Inner Plates
*Pin Diameter
*Average Tensile
*Lbs. per foot
__#40 (#425) 1/2 .312 5/16 .156 3,700 .41
__#41 1/2 .306 1/4 .141 2,000 .27
__#410 (#43) 1/2 .306 1/8 .141 1,600 .19
__#415 (#42) 1/2 .306 3/16 .141 1,600 .26
__#415H (#42H) 1/2 .306 3/16 .141 1,600 .26
__#420 1/2 .306 1/4 .156 3,700 .38
__#425 (#40) 1/2 .312 5/16 .156 3,700 .41
__#428 1/2 .335 5/16 .177 4,200 .44
__#428H 1/2 .335 5/16 .177 4,200 .44
__#520 5/8 .400 1/4 .200 6,100 .64
__#520H 5/8 .400 1/4 .200 6,100 .68
__#520-2 5/8 .400 1/4 .200 12,200 1.26
__#525 5/8 .400 5/16 .200 6,100 .65
__#530 (50) 5/8 .400 3/8 .200 6,100