Constant MAX_STANDARD_SCRIPTSIG_SIZE 

pub const MAX_STANDARD_SCRIPTSIG_SIZE: usize = 1650;

The maximum size in bytes of the scriptSig of a standard transaction input.

This is zcashd’s MAX_STANDARD_SCRIPTSIG_SIZE standardness (policy) constant: https://github.com/zcash/zcash/blob/v6.11.0/src/policy/policy.cpp#L92-L99