0.435 inches, refers to rear hole spacing for drilled and taped holes on top of the receiver.

For Pre-1964 manufactured rifles chambered in 300 H&H Magnum and 375 H&H Magnum

Winchester 70 Express Pre-1964 (.435 Rear Mount Hole Spacing for .458 Win., .416 Rem, .375 H&H, .300 Weatherby, and .300 H&H magnums)