SB 5.21.15

ratha-nīḍas tu ṣaṭ-triṁśal-lakṣa-yojanāyatas tat-turīya-bhāga-viśālas tāvān ravi-ratha-yugo yatra hayāś chando-nāmānaḥ saptāruṇa-yojitā vahanti devam ādityam.
Synonyms: 
ratha-nīḍaḥ — the interior of the chariot; tu — but; ṣaṭ-triṁśat-lakṣa-yojana-āyataḥ — 3,600,000 yojanas long; tat-turīya-bhāga — one quarter of that measure (900,000 yojanas); viśālaḥ — having a width; tāvān — so much also; ravi-ratha-yugaḥ — the yoke for the horses; yatra — where; hayāḥ — horses; chandaḥ-nāmānaḥ — having the different names of Vedic meters; sapta — seven; aruṇa-yojitāḥ — hooked up by Aruṇadeva; vahanti — carry; devam — the demigod; ādityam — the sun-god.
Translation: 
My dear King, the carriage of the sun-god’s chariot is estimated to be 3,600,000 yojanas [28,800,000 miles] long and one-fourth as wide [900,000 yojanas, or 7,200,000 miles]. The chariot’s horses, which are named after Gāyatrī and other Vedic meters, are harnessed by Aruṇadeva to a yoke that is also 900,000 yojanas wide. This chariot continuously carries the sun-god.
Purport: 

In the Viṣṇu Purāṇa it is stated:

gāyatrī ca bṛhaty uṣṇig
 jagatī triṣṭup eva ca
anuṣṭup paṅktir ity uktāś
 chandāṁsi harayo raveḥ

The seven horses yoked to the sun-god’s chariot are named Gāyatrī, Bṛhati, Uṣṇik, Jagatī, Triṣṭup, Anuṣṭup and Paṅkti. These names of various Vedic meters designate the seven horses that carry the sun-god’s chariot.