You said 501's. Did you mean 510 threaded?
Just about all standard cartomizers are the same diameter, and differ only in their length (standard size = 35mm; XL cartos are 45mm), their threading to attach to your battery device's connector (ie, 510 or 801 threads), and single or dual coils (atomizer or heating coils).
If you own a battery device that uses an 801 connector and already use 801 cartomizers (ie Ikenvape 801 Fusions), they will fit in a cartotank that was designed for a 510 cartomizer. However, the extensioned base of the 801 cartomizers will cause a gap between the bottom cap of the tank and the battery device.
Ikenvape sells both 510 and 801 threaded cartomizers, and advertises a Fusion tank to be used with their Fusion cartomizers, so perhaps that gap I was talking about above is not a factor when using this combination. Although I have used the 801 Fusion cartomizers in regular cartotanks (and dealt with the gap, I don't own the Fusion tank to know how it works with the 801 threaded cartomizers.
https://www.ikenvape.com/ProductDetails.asp?ProductCode=FUZETNK
Hopefully I understood your question and gave you useful information.