Are there any differences in the components or construction of keychain minifigs compared with regular minifigs from sets?
A minifig on a keychain and a regular minifig are essentially the same. They are made of the same components. A couple of additional procedures turn regular minifigs into keychain minifigs.
1.) There is a long screw inserted through the head and neck-post of the minifig to be able to attach the keychain to the loop at the end of the screw. If you remove the screw, there will be a small hole left inside the stud on the head, and on the neck-post.
2.) The leg assembly is fused to the torso assembly to make sure they don't separate during use as a keychain.
In addition, keychain minifigs are made in China, so there is a slight difference in how they look. The plastic has a duller and sometimes a bit more opaque appearance compared to regular minifigs. The printing, however, is the same quality, which is what most people focus on. The difference in the shine/opaqueness is usually only noticed when the keychain minifigs is placed next to an identical regular minifig.
1Do we know if the legs are glued on or if the plastic is molded differently to make it more resilient?– chicksFeb 1, 2019 at 17:26
pretty interesting. Does the slight difference of China figs also apply to figs from the 90ties?– fabianFeb 1, 2019 at 17:27
1The plastic pieces for the torso and legs are exactly the same as regular minifigs. They are not glued, but the legs are fused to the torso with a solvent, that actually loosens the surface of the ABS plastic and allows the molecules to combine. Once the solvent evaporates, it leaves behind a cleanly fused surface with no residue at all. Feb 1, 2019 at 18:12
4LEGO has been using two types of solvents through the years to "glue" minifigs, sculptures, etc. One is called MEK (methyl-ethyl-ketone) and at some point they switched to GBL (gamma-butyrolactone). Feb 1, 2019 at 18:14
2@Fabian, the collectible minifig series didn't start until 2010. At that time, LEGO didn't have their own factory in China, but worked with a partner. Now they have their own factory and are more in control of the quality. According to the official LEGO history site, lego.com/en-us/themes/lego-history LEGO didn't start working with Chinese partners until the 2000s, although it is possible that some of their non-brick items were made there even before (stationary, school-supplies, home décor, etc.) Feb 1, 2019 at 18:20