Millisats (0.001) is the result of a constant in the LN code.
 
https://github.com/lightningnetwork/lnd/blob/master/lnwire/msat.go#L10-L12

I'm not sure if that means the LN protocol cannot be divisible further.  I suspect a future version could, but the current LN protocol could not go below a millisat.

Thanks 

Just wasn’t clear if it was infinitely divisible 🙂

allark

A satoshi is the smallest unit for bitcoin, but lightning can transact with even smaller units while channels are open. The amount is rounded down to the nearest satoshi when the channel is closed and broadcast to the blockchain to adhere to bitcoins limit.

bitcoin

Is a Satoshi infinitely divisible?

> A satoshi is the smallest unit for bitcoin, but lightning can transact with even smaller units while channels are open. The amount is rounded down to the nearest satoshi when the channel is closed and broadcast to the blockchain to adhere to bitcoins limit.

https://bitcoin.stackexchange.com/a/69704