Wireline tools come in a wide range of sizes and configurations, and they don't necessarily all fit together. Size and thread are the most common variations, and a mismatch in either category can leave weak seals between various parts or even prevent them from working altogether. Crossovers serve as adapters between two disparate connections, enabling them to fit together securely. 

Crossovers function in the same manner as most types of adapters. One end of the tool matches the size and thread of one piece, while the other end matches the second piece to be connected. Although the two pieces wouldn't fit together on their own, crossovers make that connection possible. 

While this may seem like a trivial thing, it can actually be highly beneficial for your business. Crossovers enable you to connect parts and tools across brands and styles, so you won't be locked into one particular option. This way, you'll be able to purchase the downline tools and equipment that make the most sense for your needs and budget, not solely those that are an exact match for your existing hardware. This will give you a lot more flexibility and choice in selecting your oilfield tools.