Catalytic converters can be worth their weight in gold. In fact, when the metal market crashes, only the rhodium, palladium, platinum and gold in these car parts is worth extracting. The outer steel casing is only worth throwing into a pile with other steels to be melted down and recycled.
Small foreigns are appropriately named, as these converters come off of compact non-American-origin vehicles. These converters are usually small and lightweight and may lack a "honeycomb" pattern on the outside. Due to the steel grille on the inside part of the exhaust pipe on these converters, they must be busted in half to obtain the precious metals within. Some older small foreigns may have silver in them instead of gold and may lack rhodium entirely.
Large foreigns are named as such because these converters come off of luxury-sized and larger non-American-origin vehicles. These converters may weigh up to 22.7kg. each and are often bolted and welded to the underside of the vehicle, requiring a standard reciprocating saw and a sledgehammer to remove them. Large foreign catalytic converters have a steel grille on the inside of the exhaust pipe and must be broken apart to retrieve the metal within. Though gold is usually in short supply in most large foreign models, these are full of platinum and rhodium.
GM, or General Motors, catalytic converters come from vehicles that are made under the General Motors name, such as Chevrolet or GMC. These converters come from all sizes of vehicle made by this company. Because these converters lack a steel grille inside the exhaust pipe, inserting a thin, solid metal rod into one end of the exhaust pipe and pounding it against the metal inside will work to extract the precious metals. GM catalytic converters are often found to contain mostly platinum and palladium.
BMW catalytic converters come from vehicles with the same name. These are not classified as large foreigns, despite their overseas origin, because of their structure. These catalytic converters are often made in a Y-shape, with three "honeycomb" areas in total to extract metal from. Though these models don't have a steel grille inside the exhaust pipes, it's difficult to extract the precious metals from these catalytic converters without breaking them apart. Smashing them with a sledgehammer will often open one side enough so you can pry out the metal within.
Ford catalytic converters are found in cars made by Ford, such as Ford or Mercury vehicles. These catalytic converters are often quite heavy and filled with mostly rhodium. Since these converters don't have a metal grille on the inside of the exhaust pipe, they may be extracted in the same manner as GM models.