Many custom saber companies design lightsabers that can be connected together with a coupler to create a Darth Maul style double-bladed lightsaber or saberstaff. Lightsaber enthusiasts like the idea of lining up the buttons and Covertec wheels of the two hilts, simply because a double-bladed lightsaber with aligned buttons looks better than a lightsaber with unaligned buttons.
Watch How do you line up the buttons on a double-bladed lightsaber? on YouTube
Never assume that the buttons on the two lightsaber hilts will line up with all styles of couplers. If you want to ensure that the buttons will line up, you need to get a specific type of coupler called an adjustable coupler. An adjustable coupler is often more expensive than a more basic coupler and is comprised of multiple parts rather than just one piece. A coupler will be designated as ‘adjustable’ in the product title, product description or both. If you have any doubts whether a certain coupler style is adjustable, ask the seller.
In the image at the top of the page, the left double-bladed lightsaber uses a basic, non-adjustable coupler (an Ultrasabers Standard MHS Coupler [NO SOUND]) and the right double-bladed lightsaber uses an adjustable coupler (a Sabertrio Coupler Silver Black).
Consider that not all couplers among different lightsaber companies are compatible with each other. For example, an Ultrasabers coupler is NOT compatible Saberforge lightsabers. Make sure that you get a compatible coupler based on which ever brand you’re purchasing.