Karayar gajiya yana daya daga cikin manyan nau'ikan karaya na sassan karfe. Tun lokacin da Wöhler ya buga aikin gajiyawa na yau da kullun, an yi cikakken nazarin abubuwan gajiyar kayan aiki daban-daban lokacin da aka gwada su a ƙarƙashin nau'ikan nau'ikan nau'ikan yanayi da yanayin muhalli. Duk da cewa yawancin injiniyoyi da masu zane-zane sun lura da matsalolin gajiya, kuma an tattara bayanai masu yawa na gwaji, har yanzu akwai kayan aiki da injina da yawa waɗanda ke fama da karaya.
Akwai nau'i-nau'i da yawa na gazawar karayar gajiya na sassan injina:
*Tare da nau'ikan nau'ikan nau'ikan nau'ikan nau'ikan nau'ikan daban-daban, ana iya raba shi zuwa: tashin hankali da gajiyawar matsawa, gajiyawar lankwasa, gajiyawar juzu'i, gajiyawar saduwa, gajiyawar girgiza, da sauransu;
*Dangane da girman jimlar yawan karayar gajiya (Nf), ana iya raba shi zuwa: gajiya mai girma (Nf＞10⁵) da ƙarancin gajiya (Nf＜10⁴);
* Dangane da yanayin zafi da matsakaicin yanayin sassan da ke cikin sabis, ana iya raba shi zuwa: gajiyar injina (zazzabi na yau da kullun, gajiya a cikin iska), ƙarancin zafin jiki, ƙarancin zafin jiki, sanyi da gajiya mai zafi da gajiyar lalata.
Amma akwai nau'o'i na asali guda biyu kawai, wato, gajiya mai tsauri da ke haifar da damuwa mai tsanani da kuma raunin karaya na al'ada da damuwa na al'ada. Sauran nau'o'in karayar gajiya sune hadaddiyar wadannan nau'ikan asali guda biyu a karkashin yanayi daban-daban.
Karyewar sassa da yawa mafi yawa raunin gajiya ne na juyawa. A lokacin karayar gajiya mai jujjuyawa, yankin tushen gajiya gabaɗaya yana bayyana a saman, amma babu ƙayyadadden wuri, kuma adadin tushen gajiya yana iya zama ɗaya ko fiye. Matsayin dangi na yankin tushen gajiya da yankin karaya na ƙarshe koyaushe ana jujjuya su ta wani kusurwa dangane da jujjuyawar shaft. Daga wannan, ana iya ƙaddamar da jagorancin juyawa na shaft daga matsayi na dangi na yankin tushen gajiya da kuma yanki na ƙarshe.
Lokacin da akwai babban damuwa a saman shaft, yankuna tushen gajiya da yawa na iya bayyana. A wannan lokaci yankin karaya na ƙarshe zai matsa zuwa cikin shaft ɗin.
