DTH Adapter Subs & Crossover Subs

What Are DTH Adapter Subs and Crossover Subs?

A DTH adapter sub is a threaded connection component used within a DTH drill string to connect drill pipes, DTH hammers, rotary heads, and other drilling tools when the adjoining components cannot be connected directly or when a specific tool-string arrangement is required.

A DTH crossover sub is a type of adapter sub used when the two connected components have different thread sizes, thread series, or connection specifications. The term adapter sub describes the broader product category, while crossover sub emphasizes the conversion between two different connections.

The correct product must match both adjoining components. Selection should not be based only on one thread name, nominal hammer size, or outside diameter.

Pin-to-Box, Pin-to-Pin, and Box-to-Box Connection Structures

DTH adapter subs are first classified by the connection gender at each end. A pin-to-box adapter sub has one male-thread end and one female-thread end. A pin-to-pin adapter sub has male threads at both ends and connects two components with box connections. A box-to-box adapter sub has female threads at both ends and connects two components with pin connections.

Each of these three structures may use matching thread specifications or different thread specifications. Therefore, crossover subs are not limited to pin-to-box designs. Pin-to-pin and box-to-box products are also crossover configurations when the two end threads differ.

Connection gender and thread specification must be checked separately. Two ends may have the correct pin-and-box direction but still be incompatible because their thread sizes or thread series are different.

When Is a DTH Crossover Sub Required?

In DTH drilling, a crossover sub is required when two drill-string components cannot connect directly because their connection specifications do not match. The difference may involve thread size, thread series, connection gender, or another dimensional requirement.

Typical connection positions include a drill pipe and DTH hammer, a rotary head and drill pipe, or two components in a customized drilling tool string. The complete thread designation and connection direction at both ends must be confirmed before the crossover sub is produced.

A crossover sub should not be used to compensate for an unidentified, worn, or damaged thread. Existing connections should be confirmed from reliable specifications, measurements, drawings, or a sample before manufacturing.

How to Match Both Connection Ends

Start by identifying the component connected to each end of the adapter. A drilling component with a pin connection requires a box end on the adapter, while a component with a box connection requires a pin end. After confirming the connection gender, record the complete thread designation for both ends.

Outside diameter and overall length must also suit the available tool-string space and the surrounding components. Two adapter subs with the same thread combination may still require different diameters or lengths according to the drilling system.

When replacing an existing DTH adapter sub or crossover sub, do not rely only on its general appearance. Provide visible thread markings, accurate measurements, technical drawings, clear photographs, or the current sample whenever possible.

Custom Connections and Quotation Information

MSD can review standard and customized DTH adapter sub requirements according to the customer's drill-string configuration. Available options may include different pin-to-box, pin-to-pin, and box-to-box connection combinations, together with application-specific outside diameters and overall lengths.

For selection, customization, or a quotation, provide the complete thread designation at both ends, the component connected to each end, the required connection structure, outside-diameter and length requirements, required quantity, and any available drawing, measurement, photograph, or sample. DTH hammer, drill-pipe, and rotary-head connection information should also be supplied where applicable.

Customized DTH crossover subs remain subject to technical evaluation and production confirmation. Clear information for both connection ends helps reduce mismatch risk and allows the required adapter configuration to be checked before manufacturing.

Technical content reviewed by MSD Engineering Team. | MSD — 23+ years of rock drilling tools manufacturing expertise | ISO 9001 Certified | Exporting to 40+ countries