I don't understand your question. The MTU is set as 1500 on 99.9% of machines (ethernet) or 576 for dialup but you also have part of the 1500byte packet reserved for routing and protocol information (routing: source ip, dest ip, prev/next hop, ttl, vlan tag) so you only have ~1460 bytes of information you can send over ipv4.
Why does it matter if the packet is fragmented? You run the risk of having your application work on the majority of computers and not working on a handful if you start setting advanced network options like this. Just buffer the receive and read it in 1000 byte increments if that is your desired application behavior. There is also a TCP dont-fragment flag you can set but if the PMTU is below the nonfragmented packet size then the data cannot be sent and you will experience a connection error.