To obtain these handcuffs, you must first use this command:
/give @p minecraft:blaze_rod[minecraft:custom_model_data={strings:["handcuffs"]},minecraft:custom_name={"text":"HandCuffs","color":"dark_red","italic":false}] 1
Then, while holding the item you were given, enter this command:
/setcuffitem
!!!IMPORTANT!!! THESE COMMANDS WILL ONLY WORK ON A SERVER THAT HAS THE CuffEm PLUGIN INSTALLED.