Dalilin karkatar da daidaituwa tsakanin layin tsakiya na firam ɗin bel ɗin bel da madaidaiciyar madaidaiciyar mai ɗaukar bel ɗin bai kamata ya wuce 3mm ba. Dalilin karkatar da flatness na tsakiyar firam zuwa ƙasa bai wuce 0.3%.
Haɗin tsakiyar firam ɗin mai ɗaukar bel zai cika waɗannan buƙatu:
(1) Dalilin karkatar da daidaituwa na tsakiyar firam na mai ɗaukar bel a kan layi ɗaya na layin layin bai kamata ya wuce 0.1% na tsawon ba;
(2) Bambance-bambancen babba, ƙananan, da tsayi na kabu na tsakiyar firam na mai ɗaukar bel bai kamata ya wuce 1 mm ba;
(3) Kuskuren tazarar L na tsakiyar firam na mai ɗaukar bel ɗin bai kamata ya wuce ± 1.5mm ba, kuma bambancin haɓakar dangi bai kamata ya wuce 0.2% na tazara ba;
(4) Dalilin karkatar da daidaiton abin nadi na buffer mara amfani a kan layin tsakiyar zuwa layin tsakiyar tsaye na mai ɗaukar bel bai kamata ya wuce 3 mm ba.

Matsayin abin nadi bayan an haɗa mai ɗaukar bel ɗin, bisa ga hanyar na'urar ta tashin hankali, kayan bel ɗin core, tsayin bel, da tsarin birki an bayyana su a sarari, kuma gabaɗaya yakamata ya dace da buƙatun masu zuwa:
(1) Don na'urorin tayar da hankali na tsaye ko nau'in mota, bugun bugun gaba bai kamata ya zama ƙasa da 400mm ba, kuma bugun bugun gaba na baya.
Ya kamata ya zama sau 1.5 ~ 5 na bugun jini na gaba (lokacin da tsawon polyester, bel ɗin zane ko mai ɗaukar bel ya wuce 200m, kuma lokacin da aka fara motar kai tsaye kuma akwai tsarin birki na bugun jini, ya kamata a zaɓi matsakaicin ƙarfin bugun jini).
(2) Don na'urar tayar da hankali na mai ɗaukar bel, bugun bugun gaba bai kamata ya zama ƙasa da mm 100 ba.
(3) Wurin tsaftacewa na na'urar tsaftacewa ya kamata ya kasance cikin hulɗa tare da bel mai ɗaukar hoto, kuma tsayin lamba bai kamata ya zama ƙasa da 85% na fadin bel ba.
Bayan an ɗora abin nadi a kan firam ɗin jigilar bel, ya kamata ya juya a hankali kuma ana iya daidaita shi da wanki. Silindricity na axial na abin nadi mai raɗaɗi zuwa tsakiyar layinsa bayan shigarwa: lokacin da diamita mara amfani D<800Mm, juriyar girmansa shine 0.60mm; lokacin D>800Mm, juriyar girmansa shine 1.00mm. Bayan an saita mai raɗaɗi akan firam ɗin, juriyar juriya ta tsaye tsakanin layinta na tsakiya da tsakiyar layin firam shine 0.2%. Jirgin saman da ke kwance na tsakiyar simintin mai raɗaɗi ya kamata ya zo ya zo tare da tsakiyar layin firam, kuma juriyar girmansa shine 6 mm.