FASTEN, FIX, ATTACH, AFFIX mean to make something stay firmly in place.

FASTEN implies an action such as tying, buttoning, nailing, locking, or otherwise securing.

e.g. fasten the reins to a post

FIX usually implies a driving in, implanting, or embedding.

e.g. fixed the stake in the ground

ATTACH suggests a connecting or uniting by a bond, link, or tie in order to keep things together.

e.g. attach the W-2 form here

AFFIX implies an imposing of one thing on another by gluing, impressing, or nailing.

e.g. affix your address label here

source: [一眼レフカメラの本体にレンズをねじって取り付けるGIF画像｜無料GIF画像検索 GIFMAGAZINE 71362]

verb with object

1. fasten; join:

〖attach A to B〗 AをBに付ける, 貼り付ける, AをB〈機器など〉に接続する［つなげる］; AをBに添える(↔ detach)

e.g. he made certain that the trailer was securely attached to the van.

fasten (a related document) to another, or to an email:

〈文書･画像など(のファイル)〉をB〈Eメールの本文など〉に添付する

e.g. I attach a copy of the memo for your information.

include (a condition) as part of an agreement:

«…に» 〈条件〉を入れる, 付け加える «to»

e.g. the Commission can attach appropriate conditions to the operation of the agreement.

(attach oneself to) join (someone or something) without being invited:

〖～ oneself〗 «…の» 仲間に入る; 【人に】懐く «to» (!時に頼まれもしないのにまとわりつくことをさす) .

e.g. they were all too ready to attach themselves to you for the whole day.

(usually be attached) appoint (someone) for special or temporary duties:

〖attach A to B〗 A〈重要性･責任など〉がBにあると考える; A〈感情･性質など〉がBに伴う

e.g. I was attached to another department.

2. (attach something to) attribute importance or value to:

e.g. he doesn't attach too much importance to radical ideas.

no object (attach to) (of importance or value) be attributed to:

«…に» 付属する, 結合する «to» .

e.g. great importance attaches to the family role.

3. Law, archaic seize (a person's property) by legal authority:

〘法〙 〈財産〉を差し押さえる.

e.g. the court attached his wages for child support.

attachable |əˈtaCHəb(ə)l| adjective

Middle English (in the sense ‘seize by legal authority’): from Old French atachier or estachier ‘fasten, fix’, based on an element of Germanic origin related to stake1; compare with attack.